diff --git a/bind/gen.go b/bind/gen.go
index 8a9889b..3d618c3 100644
--- a/bind/gen.go
+++ b/bind/gen.go
@@ -78,46 +78,59 @@
 // with the same name. Perhaps use the index from the order the package is
 // generated.
 func pkgPrefix(pkg *types.Package) string {
+	// The error type has no package
+	if pkg == nil {
+		return ""
+	}
 	return pkg.Name()
 }
 
 func (g *generator) init() {
-	g.pkgName = g.pkg.Name()
+	if g.pkg != nil {
+		g.pkgName = g.pkg.Name()
+	}
 	g.pkgPrefix = pkgPrefix(g.pkg)
 
-	scope := g.pkg.Scope()
-	hasExported := false
-	for _, name := range scope.Names() {
-		obj := scope.Lookup(name)
-		if !obj.Exported() {
-			continue
-		}
-		hasExported = true
-		switch obj := obj.(type) {
-		case *types.Func:
-			if isCallable(obj) {
-				g.funcs = append(g.funcs, obj)
+	if g.pkg != nil {
+		scope := g.pkg.Scope()
+		hasExported := false
+		for _, name := range scope.Names() {
+			obj := scope.Lookup(name)
+			if !obj.Exported() {
+				continue
 			}
-		case *types.TypeName:
-			named := obj.Type().(*types.Named)
-			switch t := named.Underlying().(type) {
-			case *types.Struct:
-				g.structs = append(g.structs, structInfo{obj, t})
-			case *types.Interface:
-				g.interfaces = append(g.interfaces, interfaceInfo{obj, t, makeIfaceSummary(t)})
+			hasExported = true
+			switch obj := obj.(type) {
+			case *types.Func:
+				if isCallable(obj) {
+					g.funcs = append(g.funcs, obj)
+				}
+			case *types.TypeName:
+				named := obj.Type().(*types.Named)
+				switch t := named.Underlying().(type) {
+				case *types.Struct:
+					g.structs = append(g.structs, structInfo{obj, t})
+				case *types.Interface:
+					g.interfaces = append(g.interfaces, interfaceInfo{obj, t, makeIfaceSummary(t)})
+				default:
+					g.otherNames = append(g.otherNames, obj)
+				}
+			case *types.Const:
+				g.constants = append(g.constants, obj)
+			case *types.Var:
+				g.vars = append(g.vars, obj)
 			default:
-				g.otherNames = append(g.otherNames, obj)
+				g.errorf("unsupported exported type for %s: %T", obj.Name(), obj)
 			}
-		case *types.Const:
-			g.constants = append(g.constants, obj)
-		case *types.Var:
-			g.vars = append(g.vars, obj)
-		default:
-			g.errorf("unsupported exported type for %s: %T", obj.Name(), obj)
 		}
-	}
-	if !hasExported {
-		g.errorf("no exported names in the package %q", g.pkg.Path())
+		if !hasExported {
+			g.errorf("no exported names in the package %q", g.pkg.Path())
+		}
+	} else {
+		// Bind the single supported type from the universe scope, error.
+		errType := types.Universe.Lookup("error").(*types.TypeName)
+		t := errType.Type().Underlying().(*types.Interface)
+		g.interfaces = append(g.interfaces, interfaceInfo{errType, t, makeIfaceSummary(t)})
 	}
 	for _, p := range g.allPkg {
 		scope := p.Scope()
@@ -150,9 +163,6 @@
 // cgoType returns the name of a Cgo type suitable for converting a value of
 // the given type.
 func (g *generator) cgoType(t types.Type) string {
-	if isErrorType(t) {
-		return g.cgoType(types.Typ[types.String])
-	}
 	switch t := t.(type) {
 	case *types.Basic:
 		switch t.Kind() {
diff --git a/bind/gengo.go b/bind/gengo.go
index cd06a04..6353a39 100644
--- a/bind/gengo.go
+++ b/bind/gengo.go
@@ -59,7 +59,7 @@
 		g.Printf(" := ")
 	}
 
-	g.Printf("%s.%s(", selectorLHS, o.Name())
+	g.Printf("%s%s(", selectorLHS, o.Name())
 	for i := 0; i < params.Len(); i++ {
 		if i > 0 {
 			g.Printf(", ")
@@ -85,16 +85,6 @@
 }
 
 func (g *goGen) genWrite(toVar, fromVar string, t types.Type, mode varMode) {
-	if isErrorType(t) {
-		g.Printf("var %s_str string\n", toVar)
-		g.Printf("if %s == nil {\n", fromVar)
-		g.Printf("    %s_str = \"\"\n", toVar)
-		g.Printf("} else {\n")
-		g.Printf("    %s_str = %s.Error()\n", toVar, fromVar)
-		g.Printf("}\n")
-		g.genWrite(toVar, toVar+"_str", types.Typ[types.String], mode)
-		return
-	}
 	switch t := t.(type) {
 	case *types.Basic:
 		switch t.Kind() {
@@ -205,7 +195,7 @@
 		g.Indent()
 		g.Printf("ref := _seq.FromRefNum(int32(refnum))\n")
 		g.genRead("_v", "v", f.Type(), modeRetained)
-		g.Printf("ref.Get().(*%s.%s).%s = _v\n", g.pkgName(g.pkg), obj.Name(), f.Name())
+		g.Printf("ref.Get().(*%s%s).%s = _v\n", g.pkgName(g.pkg), obj.Name(), f.Name())
 		g.Outdent()
 		g.Printf("}\n\n")
 
@@ -213,7 +203,7 @@
 		g.Printf("func proxy%s_%s_%s_Get(refnum C.int32_t) C.%s {\n", g.pkgPrefix, obj.Name(), f.Name(), g.cgoType(f.Type()))
 		g.Indent()
 		g.Printf("ref := _seq.FromRefNum(int32(refnum))\n")
-		g.Printf("v := ref.Get().(*%s.%s).%s\n", g.pkgName(g.pkg), obj.Name(), f.Name())
+		g.Printf("v := ref.Get().(*%s%s).%s\n", g.pkgName(g.pkg), obj.Name(), f.Name())
 		g.genWrite("_v", "v", f.Type(), modeRetained)
 		g.Printf("return _v\n")
 		g.Outdent()
@@ -228,8 +218,8 @@
 		g.genFuncSignature(m, obj.Name())
 		g.Indent()
 		g.Printf("ref := _seq.FromRefNum(int32(refnum))\n")
-		g.Printf("v := ref.Get().(*%s.%s)\n", g.pkgName(g.pkg), obj.Name())
-		g.genFuncBody(m, "v")
+		g.Printf("v := ref.Get().(*%s%s)\n", g.pkgName(g.pkg), obj.Name())
+		g.genFuncBody(m, "v.")
 		g.Outdent()
 		g.Printf("}\n\n")
 	}
@@ -242,7 +232,7 @@
 	}
 	// TODO(hyangah): non-struct pointer types (*int), struct type.
 
-	v := fmt.Sprintf("%s.%s", g.pkgName(g.pkg), o.Name())
+	v := fmt.Sprintf("%s%s", g.pkgName(g.pkg), o.Name())
 
 	// var I int
 	//
@@ -280,8 +270,8 @@
 		g.genFuncSignature(m, obj.Name())
 		g.Indent()
 		g.Printf("ref := _seq.FromRefNum(int32(refnum))\n")
-		g.Printf("v := ref.Get().(%s.%s)\n", g.pkgName(g.pkg), obj.Name())
-		g.genFuncBody(m, "v")
+		g.Printf("v := ref.Get().(%s%s)\n", g.pkgName(g.pkg), obj.Name())
+		g.genFuncBody(m, "v.")
 		g.Outdent()
 		g.Printf("}\n\n")
 	}
@@ -365,11 +355,6 @@
 }
 
 func (g *goGen) genRead(toVar, fromVar string, typ types.Type, mode varMode) {
-	if isErrorType(typ) {
-		g.genRead(toVar+"_str", fromVar, types.Typ[types.String], mode)
-		g.Printf("%s := toError(%s_str)\n", toVar, toVar)
-		return
-	}
 	switch t := typ.(type) {
 	case *types.Basic:
 		switch t.Kind() {
@@ -403,7 +388,7 @@
 			}
 			g.Printf("// Must be a Go object\n")
 			g.Printf("%s_ref := _seq.FromRefNum(int32(%s))\n", toVar, fromVar)
-			g.Printf("%s := %s_ref.Get().(*%s.%s)\n", toVar, toVar, g.pkgName(oPkg), o.Name())
+			g.Printf("%s := %s_ref.Get().(*%s%s)\n", toVar, toVar, g.pkgName(oPkg), o.Name())
 		default:
 			g.errorf("unsupported pointer type %s", t)
 		}
@@ -416,7 +401,7 @@
 			}
 			o := t.Obj()
 			oPkg := o.Pkg()
-			if !g.validPkg(oPkg) {
+			if !isErrorType(t) && !g.validPkg(oPkg) {
 				g.errorf("type %s is defined in %s, which is not bound", t, oPkg)
 				return
 			}
@@ -424,7 +409,7 @@
 			g.Printf("%s_ref := _seq.FromRefNum(int32(%s))\n", toVar, fromVar)
 			g.Printf("if %s_ref != nil {\n", toVar)
 			g.Printf("	if %s < 0 { // go object \n", fromVar)
-			g.Printf("  	 %s = %s_ref.Get().(%s.%s)\n", toVar, toVar, g.pkgName(oPkg), o.Name())
+			g.Printf("  	 %s = %s_ref.Get().(%s%s)\n", toVar, toVar, g.pkgName(oPkg), o.Name())
 			if hasProxy {
 				g.Printf("	} else { // foreign object \n")
 				g.Printf("	   %s = (*proxy%s_%s)(%s_ref)\n", toVar, pkgPrefix(oPkg), o.Name(), toVar)
@@ -456,7 +441,7 @@
 
 		switch t.Underlying().(type) {
 		case *types.Interface, *types.Struct:
-			return fmt.Sprintf("%s.%s", g.pkgName(oPkg), types.TypeString(typ, types.RelativeTo(oPkg)))
+			return fmt.Sprintf("%s%s", g.pkgName(oPkg), types.TypeString(typ, types.RelativeTo(oPkg)))
 		default:
 			g.errorf("unsupported named type %s / %T", t, t)
 		}
@@ -476,7 +461,15 @@
 // genPreamble generates the preamble. It is generated after everything
 // else, where we know which bound packages to import.
 func (g *goGen) genPreamble() {
-	g.Printf(goPreamble, g.pkg.Name(), g.pkg.Path())
+	pkgName := ""
+	pkgPath := ""
+	if g.pkg != nil {
+		pkgName = g.pkg.Name()
+		pkgPath = g.pkg.Path()
+	} else {
+		pkgName = "universe"
+	}
+	g.Printf(goPreamble, pkgName, pkgPath)
 	g.Printf("import (\n")
 	g.Indent()
 	g.Printf("_seq \"golang.org/x/mobile/bind/seq\"\n")
@@ -524,6 +517,10 @@
 // pkgName retuns the package name and adds the package to the list of
 // imports.
 func (g *goGen) pkgName(pkg *types.Package) string {
+	// The error type has no package
+	if pkg == nil {
+		return ""
+	}
 	g.imports[pkg.Path()] = struct{}{}
-	return pkg.Name()
+	return pkg.Name() + "."
 }
diff --git a/bind/genjava.go b/bind/genjava.go
index 0364b58..4099260 100644
--- a/bind/genjava.go
+++ b/bind/genjava.go
@@ -199,12 +199,6 @@
 
 // jniType returns a string that can be used as a JNI type.
 func (g *javaGen) jniType(T types.Type) string {
-	if isErrorType(T) {
-		// The error type is usually translated into an exception in
-		// Java, however the type can be exposed in other ways, such
-		// as an exported field.
-		return g.jniType(types.Typ[types.String])
-	}
 	switch T := T.(type) {
 	case *types.Basic:
 		switch T.Kind() {
@@ -305,7 +299,7 @@
 	case *types.Named:
 		n := T.Obj()
 		nPkg := n.Pkg()
-		if !g.validPkg(nPkg) {
+		if !isErrorType(T) && !g.validPkg(nPkg) {
 			g.errorf("type %s is in %s, which is not bound", n.Name(), nPkg)
 			break
 		}
@@ -442,10 +436,6 @@
 }
 
 func (g *javaGen) genJavaToC(varName string, t types.Type, mode varMode) {
-	if isErrorType(t) {
-		g.genJavaToC(varName, types.Typ[types.String], mode)
-		return
-	}
 	switch t := t.(type) {
 	case *types.Basic:
 		switch t.Kind() {
@@ -481,10 +471,6 @@
 }
 
 func (g *javaGen) genCToJava(toName, fromName string, t types.Type, mode varMode) {
-	if isErrorType(t) {
-		g.genCToJava(toName, fromName, types.Typ[types.String], mode)
-		return
-	}
 	switch t := t.(type) {
 	case *types.Basic:
 		switch t.Kind() {
@@ -530,7 +516,7 @@
 
 func (g *javaGen) genFromRefnum(toName, fromName string, t types.Type, o *types.TypeName) {
 	oPkg := o.Pkg()
-	if !g.validPkg(oPkg) {
+	if !isErrorType(o.Type()) && !g.validPkg(oPkg) {
 		g.errorf("type %s is defined in package %s, which is not bound", t, oPkg)
 		return
 	}
@@ -555,6 +541,9 @@
 	if g.javaPkg != "" {
 		return g.javaPkg
 	}
+	if pkg == nil {
+		return "go"
+	}
 	s := javaNameReplacer.Replace(pkg.Name())
 	// Look for Java keywords that are not Go keywords, and avoid using
 	// them as a package name.
@@ -581,6 +570,9 @@
 }
 
 func className(pkg *types.Package) string {
+	if pkg == nil {
+		return "Universe"
+	}
 	return strings.Title(javaNameReplacer.Replace(pkg.Name()))
 }
 
@@ -741,10 +733,6 @@
 
 // genRelease cleans up arguments that weren't copied in genJavaToC.
 func (g *javaGen) genRelease(varName string, t types.Type, mode varMode) {
-	if isErrorType(t) {
-		g.genRelease(varName, types.Typ[types.String], mode)
-		return
-	}
 	switch t := t.(type) {
 	case *types.Basic:
 	case *types.Slice:
@@ -801,9 +789,9 @@
 			rets = append(rets, retName)
 		}
 		if res.Len() == 2 || isErrorType(t) {
-			g.Printf("jstring exc = go_seq_get_exception_message(env);\n")
-			st := types.Typ[types.String]
-			g.genJavaToC("exc", st, modeRetained)
+			g.Printf("jobject exc = go_seq_wrap_exception(env);\n")
+			errType := types.Universe.Lookup("error").Type()
+			g.genJavaToC("exc", errType, modeRetained)
 			retName = "_exc"
 			rets = append(rets, "_exc")
 		}
@@ -824,7 +812,11 @@
 }
 
 func (g *javaGen) genH() error {
-	g.Printf(hPreamble, g.gobindOpts(), g.pkg.Path(), g.className())
+	pkgPath := ""
+	if g.pkg != nil {
+		pkgPath = g.pkg.Path()
+	}
+	g.Printf(hPreamble, g.gobindOpts(), pkgPath, g.className())
 	for _, iface := range g.interfaces {
 		g.Printf("extern jclass proxy_class_%s_%s;\n", g.pkgPrefix, iface.obj.Name())
 		g.Printf("extern jmethodID proxy_class_%s_%s_cons;\n", g.pkgPrefix, iface.obj.Name())
@@ -850,9 +842,6 @@
 }
 
 func (g *javaGen) jniCallType(t types.Type) string {
-	if isErrorType(t) {
-		return g.jniCallType(types.Typ[types.String])
-	}
 	switch t := t.(type) {
 	case *types.Basic:
 		switch t.Kind() {
@@ -897,9 +886,6 @@
 }
 
 func (g *javaGen) jniSigType(T types.Type) string {
-	if isErrorType(T) {
-		return g.jniSigType(types.Typ[types.String])
-	}
 	switch T := T.(type) {
 	case *types.Basic:
 		switch T.Kind() {
@@ -943,11 +929,20 @@
 }
 
 func (g *javaGen) genC() error {
-	g.Printf(cPreamble, g.gobindOpts(), g.pkg.Path(), g.pkg.Name())
-	g.Printf("#include %q\n", g.pkg.Name()+".h")
-	for _, pkg := range g.pkg.Imports() {
-		if g.validPkg(pkg) {
-			g.Printf("#include \"%s.h\"\n", pkg.Name())
+	var pkgName, pkgPath string
+	if g.pkg != nil {
+		pkgName = g.pkg.Name()
+		pkgPath = g.pkg.Path()
+	} else {
+		pkgName = "universe"
+	}
+	g.Printf(cPreamble, g.gobindOpts(), pkgPath)
+	g.Printf("#include %q\n", pkgName+".h")
+	if g.pkg != nil {
+		for _, pkg := range g.pkg.Imports() {
+			if g.validPkg(pkg) {
+				g.Printf("#include \"%s.h\"\n", pkg.Name())
+			}
 		}
 	}
 	g.Printf("\n")
@@ -1035,16 +1030,22 @@
 }
 
 func (g *javaGen) genJava() error {
-	g.Printf(javaPreamble, g.javaPkgName(g.pkg), g.className(), g.gobindOpts(), g.pkg.Path())
+	pkgPath := ""
+	if g.pkg != nil {
+		pkgPath = g.pkg.Path()
+	}
+	g.Printf(javaPreamble, g.javaPkgName(g.pkg), g.className(), g.gobindOpts(), pkgPath)
 
 	g.Printf("public abstract class %s {\n", g.className())
 	g.Indent()
 	g.Printf("static {\n")
 	g.Indent()
 	g.Printf("Seq.touch(); // for loading the native library\n")
-	for _, p := range g.pkg.Imports() {
-		if g.validPkg(p) {
-			g.Printf("%s.%s.touch();\n", g.javaPkgName(p), className(p))
+	if g.pkg != nil {
+		for _, p := range g.pkg.Imports() {
+			if g.validPkg(p) {
+				g.Printf("%s.%s.touch();\n", g.javaPkgName(p), className(p))
+			}
 		}
 	}
 	g.Printf("init();\n")
diff --git a/bind/genobjc.go b/bind/genobjc.go
index 7e7a8b3..219d5e0 100644
--- a/bind/genobjc.go
+++ b/bind/genobjc.go
@@ -47,6 +47,9 @@
 }
 
 func (g *objcGen) namePrefixOf(pkg *types.Package) string {
+	if pkg == nil {
+		return "GoUniverse"
+	}
 	p := g.prefix
 	if p == "" {
 		p = "Go"
@@ -55,7 +58,11 @@
 }
 
 func (g *objcGen) genGoH() error {
-	g.Printf(objcPreamble, g.pkg.Path(), g.gobindOpts(), g.pkg.Path())
+	var pkgPath string
+	if g.pkg != nil {
+		pkgPath = g.pkg.Path()
+	}
+	g.Printf(objcPreamble, pkgPath, g.gobindOpts(), pkgPath)
 	g.Printf("#ifndef __%s_H__\n", g.pkgName)
 	g.Printf("#define __%s_H__\n\n", g.pkgName)
 	g.Printf("#include <stdint.h>\n")
@@ -84,14 +91,21 @@
 }
 
 func (g *objcGen) genH() error {
-	g.Printf(objcPreamble, g.pkg.Path(), g.gobindOpts(), g.pkg.Path())
+	var pkgPath string
+	if g.pkg != nil {
+		pkgPath = g.pkg.Path()
+	}
+	g.Printf(objcPreamble, pkgPath, g.gobindOpts(), pkgPath)
 	g.Printf("#ifndef __%s_H__\n", g.namePrefix)
 	g.Printf("#define __%s_H__\n", g.namePrefix)
 	g.Printf("\n")
 	g.Printf("#include <Foundation/Foundation.h>\n")
-	for _, pkg := range g.pkg.Imports() {
-		if g.validPkg(pkg) {
-			g.Printf("#include %q\n", g.namePrefixOf(pkg)+".h")
+	g.Printf("#include \"GoUniverse.h\"\n")
+	if g.pkg != nil {
+		for _, pkg := range g.pkg.Imports() {
+			if g.validPkg(pkg) {
+				g.Printf("#include %q\n", g.namePrefixOf(pkg)+".h")
+			}
 		}
 	}
 	g.Printf("\n")
@@ -191,13 +205,21 @@
 }
 
 func (g *objcGen) genM() error {
-	g.Printf(objcPreamble, g.pkg.Path(), g.gobindOpts(), g.pkg.Path())
+	var pkgPath string
+	var errDomain string
+	if g.pkg != nil {
+		pkgPath = g.pkg.Path()
+		errDomain = "go." + pkgPath
+	} else {
+		errDomain = "go"
+	}
+	g.Printf(objcPreamble, pkgPath, g.gobindOpts(), pkgPath)
 	g.Printf("#include <Foundation/Foundation.h>\n")
 	g.Printf("#include \"seq.h\"\n")
 	g.Printf("#include \"_cgo_export.h\"\n")
 	g.Printf("#include %q\n", g.namePrefix+".h")
 	g.Printf("\n")
-	g.Printf("static NSString* errDomain = @\"go.%s\";\n", g.pkg.Path())
+	g.Printf("static NSString* errDomain = @%q;\n", errDomain)
 	g.Printf("\n")
 
 	// struct
@@ -500,9 +522,6 @@
 
 func (g *objcGen) genGetter(oName string, f *types.Var) {
 	t := f.Type()
-	if isErrorType(t) {
-		t = types.Typ[types.String]
-	}
 	g.Printf("- (%s)%s {\n", g.objcType(t), lowerFirst(f.Name()))
 	g.Indent()
 	g.Printf("int32_t refnum = go_seq_go_to_refnum(self._ref);\n")
@@ -516,9 +535,6 @@
 
 func (g *objcGen) genSetter(oName string, f *types.Var) {
 	t := f.Type()
-	if isErrorType(t) {
-		t = types.Typ[types.String]
-	}
 
 	g.Printf("- (void)set%s:(%s)v {\n", f.Name(), g.objcType(t))
 	g.Indent()
@@ -531,10 +547,6 @@
 }
 
 func (g *objcGen) genWrite(varName string, t types.Type, mode varMode) {
-	if isErrorType(t) {
-		g.genWrite(varName, types.Typ[types.String], mode)
-		return
-	}
 	switch t := t.(type) {
 	case *types.Basic:
 		switch t.Kind() {
@@ -584,22 +596,18 @@
 }
 
 func (g *objcGen) genRefRead(toName, fromName string, t types.Type) {
-	ptype := g.objcType(t)
-	g.Printf("%s %s = nil;\n", ptype, toName)
+	ptype := g.refTypeBase(t)
+	g.Printf("%s* %s = nil;\n", ptype, toName)
 	g.Printf("GoSeqRef* %s_ref = go_seq_from_refnum(%s);\n", toName, fromName)
 	g.Printf("if (%s_ref != NULL) {\n", toName)
 	g.Printf("	%s = %s_ref.obj;\n", toName, toName)
 	g.Printf("	if (%s == nil) {\n", toName)
-	g.Printf("		%s = [[%s alloc] initWithRef:%s_ref];\n", toName, g.refTypeBase(t), toName)
+	g.Printf("		%s = [[%s alloc] initWithRef:%s_ref];\n", toName, ptype, toName)
 	g.Printf("	}\n")
 	g.Printf("}\n")
 }
 
 func (g *objcGen) genRead(toName, fromName string, t types.Type, mode varMode) {
-	if isErrorType(t) {
-		g.genRead(toName, fromName, types.Typ[types.String], mode)
-		return
-	}
 	switch t := t.(type) {
 	case *types.Basic:
 		switch t.Kind() {
@@ -679,11 +687,9 @@
 	if !s.returnsVal() {
 		for _, p := range s.retParams {
 			if isErrorType(p.typ) {
-				g.Printf("if ([_%s length] != 0 && %s != nil) {\n", p.name, p.name)
+				g.Printf("if (_%s != nil && %s != nil) {\n", p.name, p.name)
 				g.Indent()
-				g.Printf("NSMutableDictionary* details = [NSMutableDictionary dictionary];\n")
-				g.Printf("[details setValue:_%s forKey:NSLocalizedDescriptionKey];\n", p.name)
-				g.Printf("*%s = [NSError errorWithDomain:errDomain code:1 userInfo:details];\n", p.name)
+				g.Printf("*%s = go_seq_to_nserror(_%s, errDomain);\n", p.name, p.name)
 				g.Outdent()
 				g.Printf("}\n")
 			} else {
@@ -695,7 +701,7 @@
 	if n := len(s.retParams); n > 0 {
 		p := s.retParams[n-1]
 		if isErrorType(p.typ) {
-			g.Printf("return ([_%s length] == 0);\n", p.name)
+			g.Printf("return (_%s == nil);\n", p.name)
 		} else {
 			g.Printf("return _%s;\n", p.name)
 		}
@@ -781,7 +787,7 @@
 	g.Indent()
 	g.Printf("@autoreleasepool {\n")
 	g.Indent()
-	g.Printf("%s o = go_seq_objc_from_refnum(refnum);\n", g.objcType(obj.Type()))
+	g.Printf("%s* o = go_seq_objc_from_refnum(refnum);\n", g.refTypeBase(obj.Type()))
 	for _, p := range s.params {
 		g.genRead("_"+p.name, p.name, p.typ, modeTransient)
 	}
@@ -812,23 +818,18 @@
 			var rets []string
 			for i, p := range s.retParams {
 				if isErrorType(p.typ) {
-					g.Printf("NSString *%s_str = nil;\n", p.name)
+					g.Printf("GoUniverseerror* _%s = nil;\n", p.name)
 					if i == len(s.retParams)-1 { // last param.
 						g.Printf("if (!returnVal) {\n")
 					} else {
 						g.Printf("if (%s != nil) {\n", p.name)
 					}
 					g.Indent()
-					g.Printf("%[1]s_str = [%[1]s localizedDescription];\n", p.name)
-					g.Printf("if (%[1]s_str == nil || %[1]s_str.length == 0) {\n", p.name)
-					g.Indent()
-					g.Printf("%[1]s_str = @\"gobind: unknown error\";\n", p.name)
+					g.Printf("_%[1]s = [[goSeqErrorWrapper alloc] initWithError:%[1]s];\n", p.name)
 					g.Outdent()
 					g.Printf("}\n")
-					g.Outdent()
-					g.Printf("}\n")
-					g.genWrite(p.name+"_str", p.typ, modeRetained)
-					rets = append(rets, fmt.Sprintf("_%s_str", p.name))
+					g.genWrite("_"+p.name, p.typ, modeRetained)
+					rets = append(rets, "__"+p.name)
 				} else {
 					g.genWrite(p.name, p.typ, modeRetained)
 					rets = append(rets, "_"+p.name)
@@ -852,10 +853,6 @@
 
 // genRelease cleans up arguments that weren't copied in genWrite.
 func (g *objcGen) genRelease(varName string, t types.Type, mode varMode) {
-	if isErrorType(t) {
-		g.genRelease(varName, types.Typ[types.String], mode)
-		return
-	}
 	switch t := t.(type) {
 	case *types.Slice:
 		switch e := t.Elem().(type) {
@@ -955,7 +952,7 @@
 		}
 	case *types.Named:
 		n := typ.Obj()
-		if g.validPkg(n.Pkg()) {
+		if isErrorType(typ) || g.validPkg(n.Pkg()) {
 			switch typ.Underlying().(type) {
 			case *types.Interface, *types.Struct:
 				return g.namePrefixOf(n.Pkg()) + n.Name()
@@ -1031,7 +1028,7 @@
 		return "TODO"
 	case *types.Named:
 		n := typ.Obj()
-		if !g.validPkg(n.Pkg()) {
+		if !isErrorType(typ) && !g.validPkg(n.Pkg()) {
 			g.errorf("type %s is in package %s, which is not bound", n.Name(), n.Pkg().Name())
 			return "TODO"
 		}
diff --git a/bind/java/Seq.java b/bind/java/Seq.java
index fa2456f..564dd08 100644
--- a/bind/java/Seq.java
+++ b/bind/java/Seq.java
@@ -8,6 +8,8 @@
 import java.util.IdentityHashMap;
 import java.util.logging.Logger;
 
+import go.Universe;
+
 // Seq is a sequence of machine-dependent encoded values.
 // Used by automatically generated language bindings to talk to Go.
 public class Seq {
@@ -34,6 +36,7 @@
 			log.severe("LoadJNI class bad field: " + e);
 		}
 		init();
+		Universe.touch();
 	}
 
 	private static native void init();
@@ -44,8 +47,16 @@
 	private Seq() {
 	}
 
-	private static void throwException(String msg) throws Exception { // JNI helper
-		throw new Exception(msg);
+	private static void throwException(Universe.error err) throws Exception {
+		throw new Exception(err.Error());
+	}
+
+	private static Universe.error wrapThrowable(final Throwable t) {
+		return new Universe.error() {
+			@Override public String Error() {
+				return t.getMessage();
+			}
+		};
 	}
 
 	// ctx is an android.context.Context.
diff --git a/bind/java/SeqTest.java b/bind/java/SeqTest.java
index 30763f7..bab54cf 100644
--- a/bind/java/SeqTest.java
+++ b/bind/java/SeqTest.java
@@ -518,4 +518,22 @@
     };
     assertTrue("Go struct passed through Java should not be wrapped", Testpkg.CallCDupper(cdup));
   }
+
+  public void testEmptyError() {
+    try {
+      Testpkg.EmptyError();
+      fail("Empty error wasn't caught");
+    } catch (Exception e) {
+    }
+    Testpkg.EmptyErrorer empty = new Testpkg.EmptyErrorer() {
+      @Override public void EmptyError() throws Exception {
+        throw new Exception("");
+      }
+    };
+    try {
+      Testpkg.CallEmptyError(empty);
+      fail("Empty exception wasn't caught");
+    } catch (Exception e) {
+    }
+  }
 }
diff --git a/bind/java/seq.h b/bind/java/seq.h
index 1d9a798..0b336cd 100644
--- a/bind/java/seq.h
+++ b/bind/java/seq.h
@@ -38,7 +38,9 @@
 extern jobject go_seq_from_refnum(JNIEnv *env, int32_t refnum, jclass proxy_class, jmethodID proxy_cons);
 
 extern void go_seq_maybe_throw_exception(JNIEnv *env, jobject msg);
-extern jstring go_seq_get_exception_message(JNIEnv *env);
+// go_seq_wrap_exception wraps a pending exception in a Java object implementing the
+// golang/x/mobile/bind/errors.Error interface. If there is no pending exception, it returns NULL.
+extern jobject go_seq_wrap_exception(JNIEnv *env);
 
 extern jbyteArray go_seq_to_java_bytearray(JNIEnv *env, nbyteslice s, int copy);
 extern nbyteslice go_seq_from_java_bytearray(JNIEnv *env, jbyteArray s, int copy);
diff --git a/bind/java/seq_android.c.support b/bind/java/seq_android.c.support
index d02d732..b491fa5 100644
--- a/bind/java/seq_android.c.support
+++ b/bind/java/seq_android.c.support
@@ -30,6 +30,7 @@
 static jmethodID seq_decRef;
 static jmethodID seq_incRef;
 static jmethodID seq_incRefnum;
+static jmethodID seq_wrapThrowable;
 
 static jmethodID throwable_getMessage;
 
@@ -59,18 +60,18 @@
 }
 
 void go_seq_maybe_throw_exception(JNIEnv *env, jobject msg) {
-	if (msg != NULL && (*env)->GetStringLength(env, msg) > 0) {
+	if (msg != NULL) {
 		(*env)->CallStaticVoidMethod(env, seq_class, seq_throw_exc, msg);
 	}
 }
 
-jstring go_seq_get_exception_message(JNIEnv *env) {
+jobject go_seq_wrap_exception(JNIEnv *env) {
 	jthrowable exc = (*env)->ExceptionOccurred(env);
 	if (!exc) {
 		return NULL;
 	}
 	(*env)->ExceptionClear(env);
-	return (*env)->CallObjectMethod(env, exc, throwable_getMessage);
+	return (*env)->CallStaticObjectMethod(env, seq_class, seq_wrapThrowable, exc);
 }
 
 jbyteArray go_seq_to_java_bytearray(JNIEnv *env, nbyteslice s, int copy) {
@@ -290,7 +291,7 @@
 	}
 
 	seq_class = (*env)->NewGlobalRef(env, clazz);
-	seq_throw_exc = (*env)->GetStaticMethodID(env, seq_class, "throwException", "(Ljava/lang/String;)V");
+	seq_throw_exc = (*env)->GetStaticMethodID(env, seq_class, "throwException", "(Lgo/Universe$error;)V");
 	if (seq_throw_exc == NULL) {
 		LOG_FATAL("failed to find method Seq.throwException");
 	}
@@ -311,6 +312,10 @@
 	if (seq_incRef == NULL) {
 		LOG_FATAL("failed to find method Seq.incRef");
 	}
+	seq_wrapThrowable = (*env)->GetStaticMethodID(env, seq_class, "wrapThrowable", "(Ljava/lang/Throwable;)Lgo/Universe$error;");
+	if (seq_wrapThrowable == NULL) {
+		LOG_FATAL("failed to find method Seq.wrapThrowable");
+	}
 	jclass throwable_class = (*env)->FindClass(env, "java/lang/Throwable");
 	if (throwable_class == NULL) {
 		LOG_FATAL("failed to find Throwable class");
diff --git a/bind/objc/SeqTest.m b/bind/objc/SeqTest.m
index c36d650..7e44a97 100644
--- a/bind/objc/SeqTest.m
+++ b/bind/objc/SeqTest.m
@@ -102,6 +102,21 @@
 }
 @end
 
+// Objective-C implementation of testpkg.EmptyThrower.
+@interface EmptyErrorer: NSObject <GoTestpkgEmptyErrorer> {
+}
+
+@end
+
+@implementation EmptyErrorer {
+}
+
+- (BOOL)emptyError:(NSError **)error {
+    *error = [NSError errorWithDomain:@"SeqTest" code:1 userInfo:NULL];
+    return NO;
+}
+@end
+
 @interface tests : XCTestCase
 
 @end
@@ -406,4 +421,12 @@
 	XCTAssertTrue(GoTestpkgCallCDupper(cdup), @"Go struct passed through ObjC should not be wrapped");
 }
 
+- (void)testEmptyError {
+    NSError *error;
+    XCTAssertFalse(GoTestpkgEmptyError(&error), @"GoTestpkgEmptyError succeeded; want error");
+    XCTAssertNotNil(error, @"GoTestpkgEmptyError returned nil error");
+    id<GoTestpkgEmptyErrorer> empty = [[EmptyErrorer alloc] init];
+    XCTAssertFalse(GoTestpkgCallEmptyError(empty, &error), @"GoTestpkgCallEmptyError succeeded; want error");
+    XCTAssertNotNil(error, @"GoTestpkgCallEmptyError returned nil error");
+}
 @end
diff --git a/bind/objc/seq.h b/bind/objc/seq.h
index 1d44f8e..8941760 100644
--- a/bind/objc/seq.h
+++ b/bind/objc/seq.h
@@ -6,6 +6,7 @@
 #define __GO_SEQ_HDR__
 
 #include <Foundation/Foundation.h>
+#include "GoUniverse.h"
 
 #ifdef DEBUG
 #define LOG_DEBUG(...) NSLog(__VA_ARGS__);
@@ -23,6 +24,14 @@
                               userInfo:NULL];                                  \
   }
 
+// goErrorWrapper is a adapter between an NSError * and the bind Error interface
+@interface goSeqErrorWrapper : NSObject<GoUniverseerror> {
+}
+@property NSError *err;
+
+- (id)initWithError:(NSError *)err;
+@end
+
 // GoSeqRef is an object tagged with an integer for passing back and
 // forth across the language boundary. A GoSeqRef may represent either
 // an instance of a Go object, or an Objective-C object passed to Go.
@@ -83,5 +92,6 @@
 
 extern NSData *go_seq_to_objc_bytearray(nbyteslice, int copy);
 extern NSString *go_seq_to_objc_string(nstring str);
+extern NSError *go_seq_to_nserror(id<GoUniverseerror> err, NSString *errDomain);
 
 #endif // __GO_SEQ_HDR__
diff --git a/bind/objc/seq_darwin.m.support b/bind/objc/seq_darwin.m.support
index 917a4ef..933a35f 100644
--- a/bind/objc/seq_darwin.m.support
+++ b/bind/objc/seq_darwin.m.support
@@ -49,6 +49,22 @@
 // Note that this file is copied into and compiled with the generated
 // bindings.
 
+@implementation goSeqErrorWrapper {
+}
+@synthesize err;
+
+- (id)initWithError:(NSError *)e {
+  if (!(self = [super init]))
+    return nil;
+  self.err = e;
+  return self;
+}
+
+- (NSString *)error {
+  return [self.err localizedDescription];
+}
+@end
+
 // A simple thread-safe mutable dictionary.
 @interface goSeqDictionary : NSObject {
 }
@@ -234,6 +250,13 @@
   return res;
 }
 
+NSError *go_seq_to_nserror(id<GoUniverseerror> err, NSString *errDomain) {
+	NSString *errStr = [err error];
+	NSMutableDictionary* details = [NSMutableDictionary dictionary];
+	[details setValue:errStr forKey:NSLocalizedDescriptionKey];
+	return [NSError errorWithDomain:errDomain code:1 userInfo:details];
+}
+
 @implementation GoSeqRef {
 }
 
diff --git a/bind/seq.go.support b/bind/seq.go.support
index 2c98085..d2f36d4 100644
--- a/bind/seq.go.support
+++ b/bind/seq.go.support
@@ -13,19 +13,11 @@
 import "C"
 
 import (
-	"errors"
 	"fmt"
 
 	_seq "golang.org/x/mobile/bind/seq"
 )
 
-func toError(s string) error {
-	if s == "" {
-		return nil
-	}
-	return errors.New(s)
-}
-
 func init() {
 	_seq.FinalizeRef = func(ref *_seq.Ref) {
 		refnum := ref.Bind_Num
diff --git a/bind/testdata/basictypes.go.golden b/bind/testdata/basictypes.go.golden
index a3eb955..128aade 100644
--- a/bind/testdata/basictypes.go.golden
+++ b/bind/testdata/basictypes.go.golden
@@ -41,29 +41,23 @@
 }
 
 //export proxybasictypes__Error
-func proxybasictypes__Error() C.nstring {
+func proxybasictypes__Error() C.int32_t {
 	res_0 := basictypes.Error()
-	var _res_0_str string
-	if res_0 == nil {
-		_res_0_str = ""
-	} else {
-		_res_0_str = res_0.Error()
+	var _res_0 C.int32_t = _seq.NullRefNum
+	if res_0 != nil {
+		_res_0 = C.int32_t(_seq.ToRefNum(res_0))
 	}
-	_res_0 := encodeString(_res_0_str)
 	return _res_0
 }
 
 //export proxybasictypes__ErrorPair
-func proxybasictypes__ErrorPair() (C.nint, C.nstring) {
+func proxybasictypes__ErrorPair() (C.nint, C.int32_t) {
 	res_0, res_1 := basictypes.ErrorPair()
 	_res_0 := C.nint(res_0)
-	var _res_1_str string
-	if res_1 == nil {
-		_res_1_str = ""
-	} else {
-		_res_1_str = res_1.Error()
+	var _res_1 C.int32_t = _seq.NullRefNum
+	if res_1 != nil {
+		_res_1 = C.int32_t(_seq.ToRefNum(res_1))
 	}
-	_res_1 := encodeString(_res_1_str)
 	return _res_0, _res_1
 }
 
diff --git a/bind/testdata/basictypes.java.c.golden b/bind/testdata/basictypes.java.c.golden
index caa1d1e..2688464 100644
--- a/bind/testdata/basictypes.java.c.golden
+++ b/bind/testdata/basictypes.java.c.golden
@@ -36,8 +36,8 @@
 
 JNIEXPORT void JNICALL
 Java_go_basictypes_Basictypes_Error(JNIEnv* env, jclass clazz) {
-    nstring r0 = proxybasictypes__Error();
-    jstring _r0 = go_seq_to_java_string(env, r0);
+    int32_t r0 = proxybasictypes__Error();
+    jobject _r0 = go_seq_from_refnum(env, r0, proxy_class__error, proxy_class__error_cons);
     go_seq_maybe_throw_exception(env, _r0);
 }
 
@@ -45,7 +45,7 @@
 Java_go_basictypes_Basictypes_ErrorPair(JNIEnv* env, jclass clazz) {
     struct proxybasictypes__ErrorPair_return res = proxybasictypes__ErrorPair();
     jlong _r0 = (jlong)res.r0;
-    jstring _r1 = go_seq_to_java_string(env, res.r1);
+    jobject _r1 = go_seq_from_refnum(env, res.r1, proxy_class__error, proxy_class__error_cons);
     go_seq_maybe_throw_exception(env, _r1);
     return _r0;
 }
diff --git a/bind/testdata/basictypes.objc.h.golden b/bind/testdata/basictypes.objc.h.golden
index 707e6ce..637abc6 100644
--- a/bind/testdata/basictypes.objc.h.golden
+++ b/bind/testdata/basictypes.objc.h.golden
@@ -7,6 +7,7 @@
 #define __GoBasictypes_H__
 
 #include <Foundation/Foundation.h>
+#include "GoUniverse.h"
 
 FOUNDATION_EXPORT const BOOL GoBasictypesABool;
 FOUNDATION_EXPORT const double GoBasictypesAFloat;
diff --git a/bind/testdata/basictypes.objc.m.golden b/bind/testdata/basictypes.objc.m.golden
index c3ffba6..b57aabd 100644
--- a/bind/testdata/basictypes.objc.m.golden
+++ b/bind/testdata/basictypes.objc.m.golden
@@ -37,27 +37,37 @@
 }
 
 BOOL GoBasictypesError(NSError** error) {
-	nstring r0 = proxybasictypes__Error();
-	NSString *_error = go_seq_to_objc_string(r0);
-	if ([_error length] != 0 && error != nil) {
-		NSMutableDictionary* details = [NSMutableDictionary dictionary];
-		[details setValue:_error forKey:NSLocalizedDescriptionKey];
-		*error = [NSError errorWithDomain:errDomain code:1 userInfo:details];
+	int32_t r0 = proxybasictypes__Error();
+	GoUniverseerror* _error = nil;
+	GoSeqRef* _error_ref = go_seq_from_refnum(r0);
+	if (_error_ref != NULL) {
+		_error = _error_ref.obj;
+		if (_error == nil) {
+			_error = [[GoUniverseerror alloc] initWithRef:_error_ref];
+		}
 	}
-	return ([_error length] == 0);
+	if (_error != nil && error != nil) {
+		*error = go_seq_to_nserror(_error, errDomain);
+	}
+	return (_error == nil);
 }
 
 BOOL GoBasictypesErrorPair(int* ret0_, NSError** error) {
 	struct proxybasictypes__ErrorPair_return res = proxybasictypes__ErrorPair();
 	int _ret0_ = (int)res.r0;
-	NSString *_error = go_seq_to_objc_string(res.r1);
-	*ret0_ = _ret0_;
-	if ([_error length] != 0 && error != nil) {
-		NSMutableDictionary* details = [NSMutableDictionary dictionary];
-		[details setValue:_error forKey:NSLocalizedDescriptionKey];
-		*error = [NSError errorWithDomain:errDomain code:1 userInfo:details];
+	GoUniverseerror* _error = nil;
+	GoSeqRef* _error_ref = go_seq_from_refnum(res.r1);
+	if (_error_ref != NULL) {
+		_error = _error_ref.obj;
+		if (_error == nil) {
+			_error = [[GoUniverseerror alloc] initWithRef:_error_ref];
+		}
 	}
-	return ([_error length] == 0);
+	*ret0_ = _ret0_;
+	if (_error != nil && error != nil) {
+		*error = go_seq_to_nserror(_error, errDomain);
+	}
+	return (_error == nil);
 }
 
 void GoBasictypesInts(int8_t x, int16_t y, int32_t z, int64_t t, int u) {
diff --git a/bind/testdata/customprefix.objc.h.golden b/bind/testdata/customprefix.objc.h.golden
index 5c5164a..6dc2598 100644
--- a/bind/testdata/customprefix.objc.h.golden
+++ b/bind/testdata/customprefix.objc.h.golden
@@ -7,6 +7,7 @@
 #define __EXCustomprefix_H__
 
 #include <Foundation/Foundation.h>
+#include "GoUniverse.h"
 
 FOUNDATION_EXPORT void EXCustomprefixF();
 
diff --git a/bind/testdata/ignore.objc.h.golden b/bind/testdata/ignore.objc.h.golden
index 56d86d7..3515ac5 100644
--- a/bind/testdata/ignore.objc.h.golden
+++ b/bind/testdata/ignore.objc.h.golden
@@ -7,6 +7,7 @@
 #define __GoIgnore_H__
 
 #include <Foundation/Foundation.h>
+#include "GoUniverse.h"
 
 @class GoIgnoreS;
 @protocol GoIgnoreI;
diff --git a/bind/testdata/interfaces.go.golden b/bind/testdata/interfaces.go.golden
index a614c53..16baa81 100644
--- a/bind/testdata/interfaces.go.golden
+++ b/bind/testdata/interfaces.go.golden
@@ -22,17 +22,14 @@
 var _ = _seq.FromRefNum
 
 //export proxyinterfaces_Error_Err
-func proxyinterfaces_Error_Err(refnum C.int32_t) C.nstring {
+func proxyinterfaces_Error_Err(refnum C.int32_t) C.int32_t {
 	ref := _seq.FromRefNum(int32(refnum))
 	v := ref.Get().(interfaces.Error)
 	res_0 := v.Err()
-	var _res_0_str string
-	if res_0 == nil {
-		_res_0_str = ""
-	} else {
-		_res_0_str = res_0.Error()
+	var _res_0 C.int32_t = _seq.NullRefNum
+	if res_0 != nil {
+		_res_0 = C.int32_t(_seq.ToRefNum(res_0))
 	}
-	_res_0 := encodeString(_res_0_str)
 	return _res_0
 }
 
@@ -42,8 +39,15 @@
 
 func (p *proxyinterfaces_Error) Err() error {
 	res := C.cproxyinterfaces_Error_Err(C.int32_t(p.Bind_proxy_refnum__()))
-	_res_str := decodeString(res)
-	_res := toError(_res_str)
+	var _res error
+	_res_ref := _seq.FromRefNum(int32(res))
+	if _res_ref != nil {
+		if res < 0 { // go object
+			_res = _res_ref.Get().(error)
+		} else { // foreign object
+			_res = (*proxy_error)(_res_ref)
+		}
+	}
 	return _res
 }
 
@@ -194,7 +198,7 @@
 }
 
 //export proxyinterfaces__CallErr
-func proxyinterfaces__CallErr(param_e C.int32_t) C.nstring {
+func proxyinterfaces__CallErr(param_e C.int32_t) C.int32_t {
 	var _param_e interfaces.Error
 	_param_e_ref := _seq.FromRefNum(int32(param_e))
 	if _param_e_ref != nil {
@@ -205,13 +209,10 @@
 		}
 	}
 	res_0 := interfaces.CallErr(_param_e)
-	var _res_0_str string
-	if res_0 == nil {
-		_res_0_str = ""
-	} else {
-		_res_0_str = res_0.Error()
+	var _res_0 C.int32_t = _seq.NullRefNum
+	if res_0 != nil {
+		_res_0 = C.int32_t(_seq.ToRefNum(res_0))
 	}
-	_res_0 := encodeString(_res_0_str)
 	return _res_0
 }
 
diff --git a/bind/testdata/interfaces.java.c.golden b/bind/testdata/interfaces.java.c.golden
index 974e1af..f151ded 100644
--- a/bind/testdata/interfaces.java.c.golden
+++ b/bind/testdata/interfaces.java.c.golden
@@ -100,8 +100,8 @@
 JNIEXPORT void JNICALL
 Java_go_interfaces_Interfaces_CallErr(JNIEnv* env, jclass clazz, jobject e) {
     int32_t _e = go_seq_to_refnum(env, e);
-    nstring r0 = proxyinterfaces__CallErr(_e);
-    jstring _r0 = go_seq_to_java_string(env, r0);
+    int32_t r0 = proxyinterfaces__CallErr(_e);
+    jobject _r0 = go_seq_from_refnum(env, r0, proxy_class__error, proxy_class__error_cons);
     go_seq_maybe_throw_exception(env, _r0);
 }
 
@@ -115,17 +115,17 @@
 JNIEXPORT void JNICALL
 Java_go_interfaces_Interfaces_00024proxyError_Err(JNIEnv* env, jobject this) {
     int32_t o = go_seq_to_refnum(env, this);
-    nstring r0 = proxyinterfaces_Error_Err(o);
-    jstring _r0 = go_seq_to_java_string(env, r0);
+    int32_t r0 = proxyinterfaces_Error_Err(o);
+    jobject _r0 = go_seq_from_refnum(env, r0, proxy_class__error, proxy_class__error_cons);
     go_seq_maybe_throw_exception(env, _r0);
 }
 
-nstring cproxyinterfaces_Error_Err(int32_t refnum) {
+int32_t cproxyinterfaces_Error_Err(int32_t refnum) {
     JNIEnv *env = go_seq_push_local_frame(10);
     jobject o = go_seq_from_refnum(env, refnum, proxy_class_interfaces_Error, proxy_class_interfaces_Error_cons);
     (*env)->CallVoidMethod(env, o, mid_Error_Err);
-    jstring exc = go_seq_get_exception_message(env);
-    nstring _exc = go_seq_from_java_string(env, exc);
+    jobject exc = go_seq_wrap_exception(env);
+    int32_t _exc = go_seq_to_refnum(env, exc);
     go_seq_pop_local_frame(env);
     return _exc;
 }
diff --git a/bind/testdata/interfaces.java.h.golden b/bind/testdata/interfaces.java.h.golden
index a511de4..05840e8 100644
--- a/bind/testdata/interfaces.java.h.golden
+++ b/bind/testdata/interfaces.java.h.golden
@@ -11,7 +11,7 @@
 extern jclass proxy_class_interfaces_Error;
 extern jmethodID proxy_class_interfaces_Error_cons;
 
-nstring cproxyinterfaces_Error_Err(int32_t refnum);
+int32_t cproxyinterfaces_Error_Err(int32_t refnum);
 
 extern jclass proxy_class_interfaces_I;
 extern jmethodID proxy_class_interfaces_I_cons;
diff --git a/bind/testdata/interfaces.objc.go.h.golden b/bind/testdata/interfaces.objc.go.h.golden
index 3915b55..8452626 100644
--- a/bind/testdata/interfaces.objc.go.h.golden
+++ b/bind/testdata/interfaces.objc.go.h.golden
@@ -8,7 +8,7 @@
 
 #include <stdint.h>
 #include <objc/objc.h>
-nstring cproxyinterfaces_Error_Err(int32_t refnum);
+int32_t cproxyinterfaces_Error_Err(int32_t refnum);
 
 int32_t cproxyinterfaces_I_Rand(int32_t refnum);
 
diff --git a/bind/testdata/interfaces.objc.h.golden b/bind/testdata/interfaces.objc.h.golden
index 71262da..4464d81 100644
--- a/bind/testdata/interfaces.objc.h.golden
+++ b/bind/testdata/interfaces.objc.h.golden
@@ -7,6 +7,7 @@
 #define __GoInterfaces_H__
 
 #include <Foundation/Foundation.h>
+#include "GoUniverse.h"
 
 @protocol GoInterfacesError;
 @class GoInterfacesError;
diff --git a/bind/testdata/interfaces.objc.m.golden b/bind/testdata/interfaces.objc.m.golden
index 06fcd45..b28f05e 100644
--- a/bind/testdata/interfaces.objc.m.golden
+++ b/bind/testdata/interfaces.objc.m.golden
@@ -21,14 +21,19 @@
 
 - (BOOL)err:(NSError**)error {
 	int32_t refnum = go_seq_go_to_refnum(self._ref);
-	nstring r0 = proxyinterfaces_Error_Err(refnum);
-	NSString *_error = go_seq_to_objc_string(r0);
-	if ([_error length] != 0 && error != nil) {
-		NSMutableDictionary* details = [NSMutableDictionary dictionary];
-		[details setValue:_error forKey:NSLocalizedDescriptionKey];
-		*error = [NSError errorWithDomain:errDomain code:1 userInfo:details];
+	int32_t r0 = proxyinterfaces_Error_Err(refnum);
+	GoUniverseerror* _error = nil;
+	GoSeqRef* _error_ref = go_seq_from_refnum(r0);
+	if (_error_ref != NULL) {
+		_error = _error_ref.obj;
+		if (_error == nil) {
+			_error = [[GoUniverseerror alloc] initWithRef:_error_ref];
+		}
 	}
-	return ([_error length] == 0);
+	if (_error != nil && error != nil) {
+		*error = go_seq_to_nserror(_error, errDomain);
+	}
+	return (_error == nil);
 }
 
 @end
@@ -196,19 +201,24 @@
 	} else {
 		_e = go_seq_to_refnum(e);
 	}
-	nstring r0 = proxyinterfaces__CallErr(_e);
-	NSString *_error = go_seq_to_objc_string(r0);
-	if ([_error length] != 0 && error != nil) {
-		NSMutableDictionary* details = [NSMutableDictionary dictionary];
-		[details setValue:_error forKey:NSLocalizedDescriptionKey];
-		*error = [NSError errorWithDomain:errDomain code:1 userInfo:details];
+	int32_t r0 = proxyinterfaces__CallErr(_e);
+	GoUniverseerror* _error = nil;
+	GoSeqRef* _error_ref = go_seq_from_refnum(r0);
+	if (_error_ref != NULL) {
+		_error = _error_ref.obj;
+		if (_error == nil) {
+			_error = [[GoUniverseerror alloc] initWithRef:_error_ref];
+		}
 	}
-	return ([_error length] == 0);
+	if (_error != nil && error != nil) {
+		*error = go_seq_to_nserror(_error, errDomain);
+	}
+	return (_error == nil);
 }
 
 id<GoInterfacesI> GoInterfacesSeven() {
 	int32_t r0 = proxyinterfaces__Seven();
-	id<GoInterfacesI> _ret0_ = nil;
+	GoInterfacesI* _ret0_ = nil;
 	GoSeqRef* _ret0__ref = go_seq_from_refnum(r0);
 	if (_ret0__ref != NULL) {
 		_ret0_ = _ret0__ref.obj;
@@ -219,26 +229,29 @@
 	return _ret0_;
 }
 
-nstring cproxyinterfaces_Error_Err(int32_t refnum) {
+int32_t cproxyinterfaces_Error_Err(int32_t refnum) {
 	@autoreleasepool {
-		id<GoInterfacesError> o = go_seq_objc_from_refnum(refnum);
+		GoInterfacesError* o = go_seq_objc_from_refnum(refnum);
 		NSError* error = nil;
 		BOOL returnVal = [o err:&error];
-		NSString *error_str = nil;
+		GoUniverseerror* _error = nil;
 		if (!returnVal) {
-			error_str = [error localizedDescription];
-			if (error_str == nil || error_str.length == 0) {
-				error_str = @"gobind: unknown error";
-			}
+			_error = [[goSeqErrorWrapper alloc] initWithError:error];
 		}
-		nstring _error_str = go_seq_from_objc_string(error_str);
-		return _error_str;
+		int32_t __error;
+		if ([(id<NSObject>)(_error) isKindOfClass:[GoUniverseerror class]]) {
+			id<goSeqRefInterface> _error_proxy = (id<goSeqRefInterface>)(_error);
+			__error = go_seq_go_to_refnum(_error_proxy._ref);
+		} else {
+			__error = go_seq_to_refnum(_error);
+		}
+		return __error;
 	}
 }
 
 int32_t cproxyinterfaces_I_Rand(int32_t refnum) {
 	@autoreleasepool {
-		id<GoInterfacesI> o = go_seq_objc_from_refnum(refnum);
+		GoInterfacesI* o = go_seq_objc_from_refnum(refnum);
 		int32_t returnVal = [o rand];
 		int32_t _returnVal = (int32_t)returnVal;
 		return _returnVal;
@@ -261,7 +274,7 @@
 
 int32_t cproxyinterfaces_I3_F(int32_t refnum) {
 	@autoreleasepool {
-		id<GoInterfacesI3> o = go_seq_objc_from_refnum(refnum);
+		GoInterfacesI3* o = go_seq_objc_from_refnum(refnum);
 		GoInterfacesI1* returnVal = [o f];
 		int32_t _returnVal;
 		if ([(id<NSObject>)(returnVal) isKindOfClass:[GoInterfacesI1 class]]) {
@@ -276,14 +289,14 @@
 
 void cproxyinterfaces_LargerI_AnotherFunc(int32_t refnum) {
 	@autoreleasepool {
-		id<GoInterfacesLargerI> o = go_seq_objc_from_refnum(refnum);
+		GoInterfacesLargerI* o = go_seq_objc_from_refnum(refnum);
 		[o anotherFunc];
 	}
 }
 
 int32_t cproxyinterfaces_LargerI_Rand(int32_t refnum) {
 	@autoreleasepool {
-		id<GoInterfacesLargerI> o = go_seq_objc_from_refnum(refnum);
+		GoInterfacesLargerI* o = go_seq_objc_from_refnum(refnum);
 		int32_t returnVal = [o rand];
 		int32_t _returnVal = (int32_t)returnVal;
 		return _returnVal;
@@ -292,7 +305,7 @@
 
 int32_t cproxyinterfaces_SameI_Rand(int32_t refnum) {
 	@autoreleasepool {
-		id<GoInterfacesSameI> o = go_seq_objc_from_refnum(refnum);
+		GoInterfacesSameI* o = go_seq_objc_from_refnum(refnum);
 		int32_t returnVal = [o rand];
 		int32_t _returnVal = (int32_t)returnVal;
 		return _returnVal;
@@ -301,7 +314,7 @@
 
 void cproxyinterfaces_WithParam_HasParam(int32_t refnum, char p0) {
 	@autoreleasepool {
-		id<GoInterfacesWithParam> o = go_seq_objc_from_refnum(refnum);
+		GoInterfacesWithParam* o = go_seq_objc_from_refnum(refnum);
 		BOOL _p0 = p0 ? YES : NO;
 		[o hasParam:_p0];
 	}
diff --git a/bind/testdata/issue10788.objc.h.golden b/bind/testdata/issue10788.objc.h.golden
index c391329..f93df41 100644
--- a/bind/testdata/issue10788.objc.h.golden
+++ b/bind/testdata/issue10788.objc.h.golden
@@ -7,6 +7,7 @@
 #define __GoIssue10788_H__
 
 #include <Foundation/Foundation.h>
+#include "GoUniverse.h"
 
 @class GoIssue10788TestStruct;
 @protocol GoIssue10788TestInterface;
diff --git a/bind/testdata/issue10788.objc.m.golden b/bind/testdata/issue10788.objc.m.golden
index 7dc4200..1253a00 100644
--- a/bind/testdata/issue10788.objc.m.golden
+++ b/bind/testdata/issue10788.objc.m.golden
@@ -70,7 +70,7 @@
 
 void cproxyissue10788_TestInterface_DoSomeWork(int32_t refnum, int32_t s) {
 	@autoreleasepool {
-		id<GoIssue10788TestInterface> o = go_seq_objc_from_refnum(refnum);
+		GoIssue10788TestInterface* o = go_seq_objc_from_refnum(refnum);
 		GoIssue10788TestStruct* _s = nil;
 		GoSeqRef* _s_ref = go_seq_from_refnum(s);
 		if (_s_ref != NULL) {
@@ -85,7 +85,7 @@
 
 void cproxyissue10788_TestInterface_MultipleUnnamedParams(int32_t refnum, nint p0, nstring p1, int64_t p2) {
 	@autoreleasepool {
-		id<GoIssue10788TestInterface> o = go_seq_objc_from_refnum(refnum);
+		GoIssue10788TestInterface* o = go_seq_objc_from_refnum(refnum);
 		int _p0 = (int)p0;
 		NSString *_p1 = go_seq_to_objc_string(p1);
 		int64_t _p2 = (int64_t)p2;
diff --git a/bind/testdata/issue12328.go.golden b/bind/testdata/issue12328.go.golden
index 4a238f7..4dca6cc 100644
--- a/bind/testdata/issue12328.go.golden
+++ b/bind/testdata/issue12328.go.golden
@@ -22,23 +22,27 @@
 var _ = _seq.FromRefNum
 
 //export proxyissue12328_T_Err_Set
-func proxyissue12328_T_Err_Set(refnum C.int32_t, v C.nstring) {
+func proxyissue12328_T_Err_Set(refnum C.int32_t, v C.int32_t) {
 	ref := _seq.FromRefNum(int32(refnum))
-	_v_str := decodeString(v)
-	_v := toError(_v_str)
+	var _v error
+	_v_ref := _seq.FromRefNum(int32(v))
+	if _v_ref != nil {
+		if v < 0 { // go object
+			_v = _v_ref.Get().(error)
+		} else { // foreign object
+			_v = (*proxy_error)(_v_ref)
+		}
+	}
 	ref.Get().(*issue12328.T).Err = _v
 }
 
 //export proxyissue12328_T_Err_Get
-func proxyissue12328_T_Err_Get(refnum C.int32_t) C.nstring {
+func proxyissue12328_T_Err_Get(refnum C.int32_t) C.int32_t {
 	ref := _seq.FromRefNum(int32(refnum))
 	v := ref.Get().(*issue12328.T).Err
-	var _v_str string
-	if v == nil {
-		_v_str = ""
-	} else {
-		_v_str = v.Error()
+	var _v C.int32_t = _seq.NullRefNum
+	if v != nil {
+		_v = C.int32_t(_seq.ToRefNum(v))
 	}
-	_v := encodeString(_v_str)
 	return _v
 }
diff --git a/bind/testdata/issue12328.java.c.golden b/bind/testdata/issue12328.java.c.golden
index 52b110d..9830f6b 100644
--- a/bind/testdata/issue12328.java.c.golden
+++ b/bind/testdata/issue12328.java.c.golden
@@ -21,17 +21,17 @@
 }
 
 JNIEXPORT void JNICALL
-Java_go_issue12328_Issue12328_00024T_setErr(JNIEnv *env, jobject this, jstring v) {
+Java_go_issue12328_Issue12328_00024T_setErr(JNIEnv *env, jobject this, jobject v) {
     int32_t o = go_seq_to_refnum(env, this);
-    nstring _v = go_seq_from_java_string(env, v);
+    int32_t _v = go_seq_to_refnum(env, v);
     proxyissue12328_T_Err_Set(o, _v);
 }
 
-JNIEXPORT jstring JNICALL
+JNIEXPORT jobject JNICALL
 Java_go_issue12328_Issue12328_00024T_getErr(JNIEnv *env, jobject this) {
     int32_t o = go_seq_to_refnum(env, this);
-    nstring r0 = proxyissue12328_T_Err_Get(o);
-    jstring _r0 = go_seq_to_java_string(env, r0);
+    int32_t r0 = proxyissue12328_T_Err_Get(o);
+    jobject _r0 = go_seq_from_refnum(env, r0, proxy_class__error, proxy_class__error_cons);
     return _r0;
 }
 
diff --git a/bind/testdata/issue12328.objc.h.golden b/bind/testdata/issue12328.objc.h.golden
index 381beaa..6ab1b99 100644
--- a/bind/testdata/issue12328.objc.h.golden
+++ b/bind/testdata/issue12328.objc.h.golden
@@ -7,6 +7,7 @@
 #define __GoIssue12328_H__
 
 #include <Foundation/Foundation.h>
+#include "GoUniverse.h"
 
 @class GoIssue12328T;
 
diff --git a/bind/testdata/issue12328.objc.m.golden b/bind/testdata/issue12328.objc.m.golden
index 1dd7e9a..66969f4 100644
--- a/bind/testdata/issue12328.objc.m.golden
+++ b/bind/testdata/issue12328.objc.m.golden
@@ -20,16 +20,29 @@
 	return self;
 }
 
-- (NSString*)err {
+- (NSError*)err {
 	int32_t refnum = go_seq_go_to_refnum(self._ref);
-	nstring r0 = proxyissue12328_T_Err_Get(refnum);
-	NSString *_r0 = go_seq_to_objc_string(r0);
+	int32_t r0 = proxyissue12328_T_Err_Get(refnum);
+	GoUniverseerror* _r0 = nil;
+	GoSeqRef* _r0_ref = go_seq_from_refnum(r0);
+	if (_r0_ref != NULL) {
+		_r0 = _r0_ref.obj;
+		if (_r0 == nil) {
+			_r0 = [[GoUniverseerror alloc] initWithRef:_r0_ref];
+		}
+	}
 	return _r0;
 }
 
-- (void)setErr:(NSString*)v {
+- (void)setErr:(NSError*)v {
 	int32_t refnum = go_seq_go_to_refnum(self._ref);
-	nstring _v = go_seq_from_objc_string(v);
+	int32_t _v;
+	if ([(id<NSObject>)(v) isKindOfClass:[GoUniverseerror class]]) {
+		id<goSeqRefInterface> v_proxy = (id<goSeqRefInterface>)(v);
+		_v = go_seq_go_to_refnum(v_proxy._ref);
+	} else {
+		_v = go_seq_to_refnum(v);
+	}
 	proxyissue12328_T_Err_Set(refnum, _v);
 }
 
diff --git a/bind/testdata/issue12403.go.golden b/bind/testdata/issue12403.go.golden
index 699217a..eb83831 100644
--- a/bind/testdata/issue12403.go.golden
+++ b/bind/testdata/issue12403.go.golden
@@ -32,18 +32,15 @@
 }
 
 //export proxyissue12403_Parsable_ToJSON
-func proxyissue12403_Parsable_ToJSON(refnum C.int32_t) (C.nstring, C.nstring) {
+func proxyissue12403_Parsable_ToJSON(refnum C.int32_t) (C.nstring, C.int32_t) {
 	ref := _seq.FromRefNum(int32(refnum))
 	v := ref.Get().(issue12403.Parsable)
 	res_0, res_1 := v.ToJSON()
 	_res_0 := encodeString(res_0)
-	var _res_1_str string
-	if res_1 == nil {
-		_res_1_str = ""
-	} else {
-		_res_1_str = res_1.Error()
+	var _res_1 C.int32_t = _seq.NullRefNum
+	if res_1 != nil {
+		_res_1 = C.int32_t(_seq.ToRefNum(res_1))
 	}
-	_res_1 := encodeString(_res_1_str)
 	return _res_0, _res_1
 }
 
@@ -61,7 +58,14 @@
 func (p *proxyissue12403_Parsable) ToJSON() (string, error) {
 	res := C.cproxyissue12403_Parsable_ToJSON(C.int32_t(p.Bind_proxy_refnum__()))
 	res_0 := decodeString(res.r0)
-	res_1_str := decodeString(res.r1)
-	res_1 := toError(res_1_str)
+	var res_1 error
+	res_1_ref := _seq.FromRefNum(int32(res.r1))
+	if res_1_ref != nil {
+		if res.r1 < 0 { // go object
+			res_1 = res_1_ref.Get().(error)
+		} else { // foreign object
+			res_1 = (*proxy_error)(res_1_ref)
+		}
+	}
 	return res_0, res_1
 }
diff --git a/bind/testdata/issue12403.java.c.golden b/bind/testdata/issue12403.java.c.golden
index bcd7501..f7323f1 100644
--- a/bind/testdata/issue12403.java.c.golden
+++ b/bind/testdata/issue12403.java.c.golden
@@ -50,7 +50,7 @@
     int32_t o = go_seq_to_refnum(env, this);
     struct proxyissue12403_Parsable_ToJSON_return res = proxyissue12403_Parsable_ToJSON(o);
     jstring _r0 = go_seq_to_java_string(env, res.r0);
-    jstring _r1 = go_seq_to_java_string(env, res.r1);
+    jobject _r1 = go_seq_from_refnum(env, res.r1, proxy_class__error, proxy_class__error_cons);
     go_seq_maybe_throw_exception(env, _r1);
     return _r0;
 }
@@ -60,8 +60,8 @@
     jobject o = go_seq_from_refnum(env, refnum, proxy_class_issue12403_Parsable, proxy_class_issue12403_Parsable_cons);
     jstring res = (*env)->CallObjectMethod(env, o, mid_Parsable_ToJSON);
     nstring _res = go_seq_from_java_string(env, res);
-    jstring exc = go_seq_get_exception_message(env);
-    nstring _exc = go_seq_from_java_string(env, exc);
+    jobject exc = go_seq_wrap_exception(env);
+    int32_t _exc = go_seq_to_refnum(env, exc);
     cproxyissue12403_Parsable_ToJSON_return sres = {
     	_res, _exc
     };
diff --git a/bind/testdata/issue12403.java.h.golden b/bind/testdata/issue12403.java.h.golden
index 1b79ac5..2424a0d 100644
--- a/bind/testdata/issue12403.java.h.golden
+++ b/bind/testdata/issue12403.java.h.golden
@@ -15,7 +15,7 @@
 
 typedef struct cproxyissue12403_Parsable_ToJSON_return {
     nstring r0;
-    nstring r1;
+    int32_t r1;
 } cproxyissue12403_Parsable_ToJSON_return;
 struct cproxyissue12403_Parsable_ToJSON_return cproxyissue12403_Parsable_ToJSON(int32_t refnum);
 
diff --git a/bind/testdata/issue12403.objc.go.h.golden b/bind/testdata/issue12403.objc.go.h.golden
index d418219..9d4e5fc 100644
--- a/bind/testdata/issue12403.objc.go.h.golden
+++ b/bind/testdata/issue12403.objc.go.h.golden
@@ -12,7 +12,7 @@
 
 typedef struct cproxyissue12403_Parsable_ToJSON_return {
 	nstring r0;
-	nstring r1;
+	int32_t r1;
 } cproxyissue12403_Parsable_ToJSON_return;
 struct cproxyissue12403_Parsable_ToJSON_return cproxyissue12403_Parsable_ToJSON(int32_t refnum);
 
diff --git a/bind/testdata/issue12403.objc.h.golden b/bind/testdata/issue12403.objc.h.golden
index cb81a42..5b9f310 100644
--- a/bind/testdata/issue12403.objc.h.golden
+++ b/bind/testdata/issue12403.objc.h.golden
@@ -7,6 +7,7 @@
 #define __GoIssue12403_H__
 
 #include <Foundation/Foundation.h>
+#include "GoUniverse.h"
 
 @protocol GoIssue12403Parsable;
 @class GoIssue12403Parsable;
diff --git a/bind/testdata/issue12403.objc.m.golden b/bind/testdata/issue12403.objc.m.golden
index 808db2c..072dfbc 100644
--- a/bind/testdata/issue12403.objc.m.golden
+++ b/bind/testdata/issue12403.objc.m.golden
@@ -31,14 +31,19 @@
 	int32_t refnum = go_seq_go_to_refnum(self._ref);
 	struct proxyissue12403_Parsable_ToJSON_return res = proxyissue12403_Parsable_ToJSON(refnum);
 	NSString *_ret0_ = go_seq_to_objc_string(res.r0);
-	NSString *_error = go_seq_to_objc_string(res.r1);
-	*ret0_ = _ret0_;
-	if ([_error length] != 0 && error != nil) {
-		NSMutableDictionary* details = [NSMutableDictionary dictionary];
-		[details setValue:_error forKey:NSLocalizedDescriptionKey];
-		*error = [NSError errorWithDomain:errDomain code:1 userInfo:details];
+	GoUniverseerror* _error = nil;
+	GoSeqRef* _error_ref = go_seq_from_refnum(res.r1);
+	if (_error_ref != NULL) {
+		_error = _error_ref.obj;
+		if (_error == nil) {
+			_error = [[GoUniverseerror alloc] initWithRef:_error_ref];
+		}
 	}
-	return ([_error length] == 0);
+	*ret0_ = _ret0_;
+	if (_error != nil && error != nil) {
+		*error = go_seq_to_nserror(_error, errDomain);
+	}
+	return (_error == nil);
 }
 
 @end
@@ -47,7 +52,7 @@
 
 nstring cproxyissue12403_Parsable_FromJSON(int32_t refnum, nstring jstr) {
 	@autoreleasepool {
-		id<GoIssue12403Parsable> o = go_seq_objc_from_refnum(refnum);
+		GoIssue12403Parsable* o = go_seq_objc_from_refnum(refnum);
 		NSString *_jstr = go_seq_to_objc_string(jstr);
 		NSString* returnVal = [o fromJSON:_jstr];
 		nstring _returnVal = go_seq_from_objc_string(returnVal);
@@ -57,21 +62,24 @@
 
 struct cproxyissue12403_Parsable_ToJSON_return cproxyissue12403_Parsable_ToJSON(int32_t refnum) {
 	@autoreleasepool {
-		id<GoIssue12403Parsable> o = go_seq_objc_from_refnum(refnum);
+		GoIssue12403Parsable* o = go_seq_objc_from_refnum(refnum);
 		NSString* ret0_;
 		NSError* error = nil;
 		BOOL returnVal = [o toJSON:&ret0_ error:&error];
 		nstring _ret0_ = go_seq_from_objc_string(ret0_);
-		NSString *error_str = nil;
+		GoUniverseerror* _error = nil;
 		if (!returnVal) {
-			error_str = [error localizedDescription];
-			if (error_str == nil || error_str.length == 0) {
-				error_str = @"gobind: unknown error";
-			}
+			_error = [[goSeqErrorWrapper alloc] initWithError:error];
 		}
-		nstring _error_str = go_seq_from_objc_string(error_str);
+		int32_t __error;
+		if ([(id<NSObject>)(_error) isKindOfClass:[GoUniverseerror class]]) {
+			id<goSeqRefInterface> _error_proxy = (id<goSeqRefInterface>)(_error);
+			__error = go_seq_go_to_refnum(_error_proxy._ref);
+		} else {
+			__error = go_seq_to_refnum(_error);
+		}
 		cproxyissue12403_Parsable_ToJSON_return _sres = {
-		  _ret0_, _error_str
+		  _ret0_, __error
 		};
 		return _sres;
 	}
diff --git a/bind/testdata/structs.go.golden b/bind/testdata/structs.go.golden
index 32f4c9c..5f6d741 100644
--- a/bind/testdata/structs.go.golden
+++ b/bind/testdata/structs.go.golden
@@ -52,7 +52,7 @@
 }
 
 //export proxystructs_S_Identity
-func proxystructs_S_Identity(refnum C.int32_t) (C.int32_t, C.nstring) {
+func proxystructs_S_Identity(refnum C.int32_t) (C.int32_t, C.int32_t) {
 	ref := _seq.FromRefNum(int32(refnum))
 	v := ref.Get().(*structs.S)
 	res_0, res_1 := v.Identity()
@@ -60,13 +60,10 @@
 	if res_0 != nil {
 		_res_0 = C.int32_t(_seq.ToRefNum(res_0))
 	}
-	var _res_1_str string
-	if res_1 == nil {
-		_res_1_str = ""
-	} else {
-		_res_1_str = res_1.Error()
+	var _res_1 C.int32_t = _seq.NullRefNum
+	if res_1 != nil {
+		_res_1 = C.int32_t(_seq.ToRefNum(res_1))
 	}
-	_res_1 := encodeString(_res_1_str)
 	return _res_0, _res_1
 }
 
@@ -124,7 +121,7 @@
 }
 
 //export proxystructs__IdentityWithError
-func proxystructs__IdentityWithError(param_s C.int32_t) (C.int32_t, C.nstring) {
+func proxystructs__IdentityWithError(param_s C.int32_t) (C.int32_t, C.int32_t) {
 	// Must be a Go object
 	_param_s_ref := _seq.FromRefNum(int32(param_s))
 	_param_s := _param_s_ref.Get().(*structs.S)
@@ -133,12 +130,9 @@
 	if res_0 != nil {
 		_res_0 = C.int32_t(_seq.ToRefNum(res_0))
 	}
-	var _res_1_str string
-	if res_1 == nil {
-		_res_1_str = ""
-	} else {
-		_res_1_str = res_1.Error()
+	var _res_1 C.int32_t = _seq.NullRefNum
+	if res_1 != nil {
+		_res_1 = C.int32_t(_seq.ToRefNum(res_1))
 	}
-	_res_1 := encodeString(_res_1_str)
 	return _res_0, _res_1
 }
diff --git a/bind/testdata/structs.java.c.golden b/bind/testdata/structs.java.c.golden
index c5f66e2..f2417cd 100644
--- a/bind/testdata/structs.java.c.golden
+++ b/bind/testdata/structs.java.c.golden
@@ -47,7 +47,7 @@
     int32_t _s = go_seq_to_refnum(env, s);
     struct proxystructs__IdentityWithError_return res = proxystructs__IdentityWithError(_s);
     jobject _r0 = go_seq_from_refnum(env, res.r0, proxy_class_structs_S, proxy_class_structs_S_cons);
-    jstring _r1 = go_seq_to_java_string(env, res.r1);
+    jobject _r1 = go_seq_from_refnum(env, res.r1, proxy_class__error, proxy_class__error_cons);
     go_seq_maybe_throw_exception(env, _r1);
     return _r0;
 }
@@ -57,7 +57,7 @@
     int32_t o = go_seq_to_refnum(env, this);
     struct proxystructs_S_Identity_return res = proxystructs_S_Identity(o);
     jobject _r0 = go_seq_from_refnum(env, res.r0, proxy_class_structs_S, proxy_class_structs_S_cons);
-    jstring _r1 = go_seq_to_java_string(env, res.r1);
+    jobject _r1 = go_seq_from_refnum(env, res.r1, proxy_class__error, proxy_class__error_cons);
     go_seq_maybe_throw_exception(env, _r1);
     return _r0;
 }
diff --git a/bind/testdata/structs.objc.h.golden b/bind/testdata/structs.objc.h.golden
index 0b9de0e..1512cf7 100644
--- a/bind/testdata/structs.objc.h.golden
+++ b/bind/testdata/structs.objc.h.golden
@@ -7,6 +7,7 @@
 #define __GoStructs_H__
 
 #include <Foundation/Foundation.h>
+#include "GoUniverse.h"
 
 @class GoStructsS;
 @class GoStructsS2;
diff --git a/bind/testdata/structs.objc.m.golden b/bind/testdata/structs.objc.m.golden
index 25dee7e..e48173e 100644
--- a/bind/testdata/structs.objc.m.golden
+++ b/bind/testdata/structs.objc.m.golden
@@ -57,14 +57,19 @@
 			_ret0_ = [[GoStructsS alloc] initWithRef:_ret0__ref];
 		}
 	}
-	NSString *_error = go_seq_to_objc_string(res.r1);
-	*ret0_ = _ret0_;
-	if ([_error length] != 0 && error != nil) {
-		NSMutableDictionary* details = [NSMutableDictionary dictionary];
-		[details setValue:_error forKey:NSLocalizedDescriptionKey];
-		*error = [NSError errorWithDomain:errDomain code:1 userInfo:details];
+	GoUniverseerror* _error = nil;
+	GoSeqRef* _error_ref = go_seq_from_refnum(res.r1);
+	if (_error_ref != NULL) {
+		_error = _error_ref.obj;
+		if (_error == nil) {
+			_error = [[GoUniverseerror alloc] initWithRef:_error_ref];
+		}
 	}
-	return ([_error length] == 0);
+	*ret0_ = _ret0_;
+	if (_error != nil && error != nil) {
+		*error = go_seq_to_nserror(_error, errDomain);
+	}
+	return (_error == nil);
 }
 
 - (double)sum {
@@ -155,19 +160,24 @@
 			_ret0_ = [[GoStructsS alloc] initWithRef:_ret0__ref];
 		}
 	}
-	NSString *_error = go_seq_to_objc_string(res.r1);
-	*ret0_ = _ret0_;
-	if ([_error length] != 0 && error != nil) {
-		NSMutableDictionary* details = [NSMutableDictionary dictionary];
-		[details setValue:_error forKey:NSLocalizedDescriptionKey];
-		*error = [NSError errorWithDomain:errDomain code:1 userInfo:details];
+	GoUniverseerror* _error = nil;
+	GoSeqRef* _error_ref = go_seq_from_refnum(res.r1);
+	if (_error_ref != NULL) {
+		_error = _error_ref.obj;
+		if (_error == nil) {
+			_error = [[GoUniverseerror alloc] initWithRef:_error_ref];
+		}
 	}
-	return ([_error length] == 0);
+	*ret0_ = _ret0_;
+	if (_error != nil && error != nil) {
+		*error = go_seq_to_nserror(_error, errDomain);
+	}
+	return (_error == nil);
 }
 
 void cproxystructs_I_M(int32_t refnum) {
 	@autoreleasepool {
-		id<GoStructsI> o = go_seq_objc_from_refnum(refnum);
+		GoStructsI* o = go_seq_objc_from_refnum(refnum);
 		[o m];
 	}
 }
diff --git a/bind/testdata/try.objc.h.golden b/bind/testdata/try.objc.h.golden
index 62b4107..6bbd53c 100644
--- a/bind/testdata/try.objc.h.golden
+++ b/bind/testdata/try.objc.h.golden
@@ -7,6 +7,7 @@
 #define __GoTry_H__
 
 #include <Foundation/Foundation.h>
+#include "GoUniverse.h"
 
 FOUNDATION_EXPORT NSString* GoTryThis();
 
diff --git a/bind/testdata/vars.objc.h.golden b/bind/testdata/vars.objc.h.golden
index e5b24ef..33bd824 100644
--- a/bind/testdata/vars.objc.h.golden
+++ b/bind/testdata/vars.objc.h.golden
@@ -7,6 +7,7 @@
 #define __GoVars_H__
 
 #include <Foundation/Foundation.h>
+#include "GoUniverse.h"
 
 @class GoVarsS;
 @protocol GoVarsI;
diff --git a/bind/testdata/vars.objc.m.golden b/bind/testdata/vars.objc.m.golden
index dbc5fd1..4bff376 100644
--- a/bind/testdata/vars.objc.m.golden
+++ b/bind/testdata/vars.objc.m.golden
@@ -182,7 +182,7 @@
 
 + (id<GoVarsI>) anInterface {
 	int32_t r0 = var_getvars_AnInterface();
-	id<GoVarsI> _r0 = nil;
+	GoVarsI* _r0 = nil;
 	GoSeqRef* _r0_ref = go_seq_from_refnum(r0);
 	if (_r0_ref != NULL) {
 		_r0 = _r0_ref.obj;
diff --git a/bind/testpkg/testpkg.go b/bind/testpkg/testpkg.go
index 3c0c59a..881a832 100644
--- a/bind/testpkg/testpkg.go
+++ b/bind/testpkg/testpkg.go
@@ -511,3 +511,15 @@
 	got := d.CDup(want)
 	return got == want
 }
+
+type EmptyErrorer interface {
+	EmptyError() error
+}
+
+func EmptyError() error {
+	return errors.New("")
+}
+
+func CallEmptyError(c EmptyErrorer) error {
+	return c.EmptyError()
+}
diff --git a/cmd/gomobile/bind.go b/cmd/gomobile/bind.go
index 8f388c9..41e8c8d 100644
--- a/cmd/gomobile/bind.go
+++ b/cmd/gomobile/bind.go
@@ -174,19 +174,26 @@
 
 func (b *binder) GenObjc(pkg *types.Package, allPkg []*types.Package, outdir string) (string, error) {
 	const bindPrefixDefault = "Go"
-	if bindPrefix == "" {
+	if bindPrefix == "" || pkg == nil {
 		bindPrefix = bindPrefixDefault
 	}
-	name := strings.Title(pkg.Name())
+	pkgName := ""
+	pkgPath := ""
+	if pkg != nil {
+		pkgName = pkg.Name()
+		pkgPath = pkg.Path()
+	} else {
+		pkgName = "universe"
+	}
 	bindOption := "-lang=objc"
 	if bindPrefix != bindPrefixDefault {
 		bindOption += " -prefix=" + bindPrefix
 	}
 
-	fileBase := bindPrefix + name
+	fileBase := bindPrefix + strings.Title(pkgName)
 	mfile := filepath.Join(outdir, fileBase+".m")
 	hfile := filepath.Join(outdir, fileBase+".h")
-	gohfile := filepath.Join(outdir, pkg.Name()+".h")
+	gohfile := filepath.Join(outdir, pkgName+".h")
 
 	conf := &bind.GeneratorConfig{
 		Fset:   b.fset,
@@ -195,7 +202,7 @@
 	}
 	generate := func(w io.Writer) error {
 		if buildX {
-			printcmd("gobind %s -outdir=%s %s", bindOption, outdir, pkg.Path())
+			printcmd("gobind %s -outdir=%s %s", bindOption, outdir, pkgPath)
 		}
 		if buildN {
 			return nil
@@ -245,13 +252,25 @@
 }
 
 func (b *binder) GenJava(pkg *types.Package, allPkg []*types.Package, outdir, javadir string) error {
-	className := strings.Title(pkg.Name())
+	var className string
+	pkgName := ""
+	pkgPath := ""
+	javaPkg := ""
+	if pkg != nil {
+		className = strings.Title(pkg.Name())
+		pkgName = pkg.Name()
+		pkgPath = pkg.Path()
+		javaPkg = bindJavaPkg
+	} else {
+		pkgName = "universe"
+		className = "Universe"
+	}
 	javaFile := filepath.Join(javadir, className+".java")
-	cFile := filepath.Join(outdir, "java_"+pkg.Name()+".c")
-	hFile := filepath.Join(outdir, pkg.Name()+".h")
+	cFile := filepath.Join(outdir, "java_"+pkgName+".c")
+	hFile := filepath.Join(outdir, pkgName+".h")
 	bindOption := "-lang=java"
-	if bindJavaPkg != "" {
-		bindOption += " -javapkg=" + bindJavaPkg
+	if javaPkg != "" {
+		bindOption += " -javapkg=" + javaPkg
 	}
 
 	conf := &bind.GeneratorConfig{
@@ -261,13 +280,13 @@
 	}
 	generate := func(w io.Writer) error {
 		if buildX {
-			printcmd("gobind %s -outdir=%s %s", bindOption, javadir, pkg.Path())
+			printcmd("gobind %s -outdir=%s %s", bindOption, javadir, pkgPath)
 		}
 		if buildN {
 			return nil
 		}
 		conf.Writer = w
-		return bind.GenJava(conf, bindJavaPkg, bind.Java)
+		return bind.GenJava(conf, javaPkg, bind.Java)
 	}
 	if err := writeFile(javaFile, generate); err != nil {
 		return err
@@ -293,12 +312,17 @@
 }
 
 func (b *binder) GenGo(pkg *types.Package, allPkg []*types.Package, outdir string) error {
-	pkgName := "go_" + pkg.Name()
+	pkgName := "go_"
+	pkgPath := ""
+	if pkg != nil {
+		pkgName += pkg.Name()
+		pkgPath = pkg.Path()
+	}
 	goFile := filepath.Join(outdir, pkgName+"main.go")
 
 	generate := func(w io.Writer) error {
 		if buildX {
-			printcmd("gobind -lang=go -outdir=%s %s", outdir, pkg.Path())
+			printcmd("gobind -lang=go -outdir=%s %s", outdir, pkgPath)
 		}
 		if buildN {
 			return nil
diff --git a/cmd/gomobile/bind_androidapp.go b/cmd/gomobile/bind_androidapp.go
index e6d8568..60f9166 100644
--- a/cmd/gomobile/bind_androidapp.go
+++ b/cmd/gomobile/bind_androidapp.go
@@ -76,6 +76,10 @@
 				return err
 			}
 		}
+		// Generate the error type.
+		if err := binder.GenGo(nil, binder.pkgs, srcDir); err != nil {
+			return err
+		}
 
 		err = writeFile(mainFile, func(w io.Writer) error {
 			_, err := w.Write(androidMainFile)
@@ -100,6 +104,9 @@
 				return err
 			}
 		}
+		if err := binder.GenJava(nil, binder.pkgs, srcDir, filepath.Join(androidDir, "src/main/java/go")); err != nil {
+			return err
+		}
 		if err := binder.GenJavaSupport(srcDir); err != nil {
 			return err
 		}
diff --git a/cmd/gomobile/bind_iosapp.go b/cmd/gomobile/bind_iosapp.go
index 1ec010c..c4753c0 100644
--- a/cmd/gomobile/bind_iosapp.go
+++ b/cmd/gomobile/bind_iosapp.go
@@ -41,6 +41,10 @@
 			return err
 		}
 	}
+	// Generate the error type.
+	if err := binder.GenGo(nil, binder.pkgs, srcDir); err != nil {
+		return err
+	}
 	mainFile := filepath.Join(tmpdir, "src/iosbin/main.go")
 	err = writeFile(mainFile, func(w io.Writer) error {
 		_, err := w.Write(iosBindFile)
@@ -50,12 +54,15 @@
 		return fmt.Errorf("failed to create the binding package for iOS: %v", err)
 	}
 
-	fileBases := make([]string, len(typesPkgs))
+	fileBases := make([]string, len(typesPkgs)+1)
 	for i, pkg := range binder.pkgs {
 		if fileBases[i], err = binder.GenObjc(pkg, binder.pkgs, srcDir); err != nil {
 			return err
 		}
 	}
+	if fileBases[len(fileBases)-1], err = binder.GenObjc(nil, binder.pkgs, srcDir); err != nil {
+		return err
+	}
 	if err := binder.GenObjcSupport(srcDir); err != nil {
 		return err
 	}
diff --git a/cmd/gomobile/bind_test.go b/cmd/gomobile/bind_test.go
index d0b7736..51d7d60 100644
--- a/cmd/gomobile/bind_test.go
+++ b/cmd/gomobile/bind_test.go
@@ -108,11 +108,17 @@
 mkdir -p $WORK/fakegopath/pkg/android_arm/golang.org/x/mobile
 mkdir -p $WORK/gomobile_bind
 gobind -lang=go -outdir=$WORK/gomobile_bind golang.org/x/mobile/asset
+mkdir -p $WORK/gomobile_bind
+gobind -lang=go -outdir=$WORK/gomobile_bind 
 mkdir -p $WORK/androidlib
 mkdir -p $WORK/android/src/main/java/{{.JavaPkgDir}}
 {{.GobindJavaCmd}} -outdir=$WORK/android/src/main/java/{{.JavaPkgDir}} golang.org/x/mobile/asset
 mkdir -p $WORK/gomobile_bind
 mkdir -p $WORK/gomobile_bind
+mkdir -p $WORK/android/src/main/java/go
+gobind -lang=java -outdir=$WORK/android/src/main/java/go 
+mkdir -p $WORK/gomobile_bind
+mkdir -p $WORK/gomobile_bind
 cp $GOPATH/src/golang.org/x/mobile/bind/java/seq_android.go.support $WORK/gomobile_bind/seq_android.go
 mkdir -p $WORK/gomobile_bind
 cp $GOPATH/src/golang.org/x/mobile/bind/java/seq_android.c.support $WORK/gomobile_bind/seq_android.c