diff --git a/go/gcexportdata/gcexportdata.go b/go/gcexportdata/gcexportdata.go
index b44bdbf..997d3b2 100644
--- a/go/gcexportdata/gcexportdata.go
+++ b/go/gcexportdata/gcexportdata.go
@@ -92,6 +92,10 @@
 // Write writes encoded type information for the specified package to out.
 // The FileSet provides file position information for named objects.
 func Write(out io.Writer, fset *token.FileSet, pkg *types.Package) error {
-	_, err := out.Write(gcimporter.BExportData(fset, pkg))
+	b, err := gcimporter.BExportData(fset, pkg)
+	if err != nil {
+		return err
+	}
+	_, err = out.Write(b)
 	return err
 }
diff --git a/go/internal/gcimporter/bexport.go b/go/internal/gcimporter/bexport.go
index cbf8bc0..b106172 100644
--- a/go/internal/gcimporter/bexport.go
+++ b/go/internal/gcimporter/bexport.go
@@ -16,7 +16,6 @@
 	"go/constant"
 	"go/token"
 	"go/types"
-	"log"
 	"math"
 	"math/big"
 	"sort"
@@ -76,9 +75,29 @@
 	indent  int // for trace
 }
 
+// internalError represents an error generated inside this package.
+type internalError string
+
+func (e internalError) Error() string { return "gcimporter: " + string(e) }
+
+func internalErrorf(format string, args ...interface{}) error {
+	return internalError(fmt.Sprintf(format, args...))
+}
+
 // BExportData returns binary export data for pkg.
 // If no file set is provided, position info will be missing.
-func BExportData(fset *token.FileSet, pkg *types.Package) []byte {
+func BExportData(fset *token.FileSet, pkg *types.Package) (b []byte, err error) {
+	defer func() {
+		if e := recover(); e != nil {
+			if ierr, ok := e.(internalError); ok {
+				err = ierr
+				return
+			}
+			// Not an internal error; panic again.
+			panic(e)
+		}
+	}()
+
 	p := exporter{
 		fset:          fset,
 		strIndex:      map[string]int{"": 0}, // empty string is mapped to 0
@@ -107,7 +126,7 @@
 		p.typIndex[typ] = index
 	}
 	if len(p.typIndex) != len(predeclared) {
-		log.Fatalf("gcimporter: duplicate entries in type map?")
+		return nil, internalError("duplicate entries in type map?")
 	}
 
 	// write package data
@@ -145,12 +164,12 @@
 
 	// --- end of export data ---
 
-	return p.out.Bytes()
+	return p.out.Bytes(), nil
 }
 
 func (p *exporter) pkg(pkg *types.Package, emptypath bool) {
 	if pkg == nil {
-		log.Fatalf("gcimporter: unexpected nil pkg")
+		panic(internalError("unexpected nil pkg"))
 	}
 
 	// if we saw the package before, write its index (>= 0)
@@ -209,7 +228,7 @@
 		p.paramList(sig.Results(), false)
 
 	default:
-		log.Fatalf("gcimporter: unexpected object %v (%T)", obj, obj)
+		panic(internalErrorf("unexpected object %v (%T)", obj, obj))
 	}
 }
 
@@ -273,7 +292,7 @@
 
 func (p *exporter) typ(t types.Type) {
 	if t == nil {
-		log.Fatalf("gcimporter: nil type")
+		panic(internalError("nil type"))
 	}
 
 	// Possible optimization: Anonymous pointer types *T where
@@ -356,7 +375,7 @@
 		p.typ(t.Elem())
 
 	default:
-		log.Fatalf("gcimporter: unexpected type %T: %s", t, t)
+		panic(internalErrorf("unexpected type %T: %s", t, t))
 	}
 }
 
@@ -422,7 +441,7 @@
 
 func (p *exporter) field(f *types.Var) {
 	if !f.IsField() {
-		log.Fatalf("gcimporter: field expected")
+		panic(internalError("field expected"))
 	}
 
 	p.pos(f)
@@ -452,7 +471,7 @@
 func (p *exporter) method(m *types.Func) {
 	sig := m.Type().(*types.Signature)
 	if sig.Recv() == nil {
-		log.Fatalf("gcimporter: method expected")
+		panic(internalError("method expected"))
 	}
 
 	p.pos(m)
@@ -575,13 +594,13 @@
 		p.tag(unknownTag)
 
 	default:
-		log.Fatalf("gcimporter: unexpected value %v (%T)", x, x)
+		panic(internalErrorf("unexpected value %v (%T)", x, x))
 	}
 }
 
 func (p *exporter) float(x constant.Value) {
 	if x.Kind() != constant.Float {
-		log.Fatalf("gcimporter: unexpected constant %v, want float", x)
+		panic(internalErrorf("unexpected constant %v, want float", x))
 	}
 	// extract sign (there is no -0)
 	sign := constant.Sign(x)
@@ -616,7 +635,7 @@
 	m.SetMantExp(&m, int(m.MinPrec()))
 	mant, acc := m.Int(nil)
 	if acc != big.Exact {
-		log.Fatalf("gcimporter: internal error")
+		panic(internalError("internal error"))
 	}
 
 	p.int(sign)
@@ -653,7 +672,7 @@
 
 func (p *exporter) index(marker byte, index int) {
 	if index < 0 {
-		log.Fatalf("gcimporter: invalid index < 0")
+		panic(internalError("invalid index < 0"))
 	}
 	if debugFormat {
 		p.marker('t')
@@ -666,7 +685,7 @@
 
 func (p *exporter) tag(tag int) {
 	if tag >= 0 {
-		log.Fatalf("gcimporter: invalid tag >= 0")
+		panic(internalError("invalid tag >= 0"))
 	}
 	if debugFormat {
 		p.marker('t')
diff --git a/go/internal/gcimporter/bexport19_test.go b/go/internal/gcimporter/bexport19_test.go
index 0107f80..5c3cf2d 100644
--- a/go/internal/gcimporter/bexport19_test.go
+++ b/go/internal/gcimporter/bexport19_test.go
@@ -80,7 +80,10 @@
 	checkPkg(t, pkg1, "export")
 
 	// export
-	exportdata := gcimporter.BExportData(fset1, pkg1)
+	exportdata, err := gcimporter.BExportData(fset1, pkg1)
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	// import
 	imports := make(map[string]*types.Package)
diff --git a/go/internal/gcimporter/bexport_test.go b/go/internal/gcimporter/bexport_test.go
index 4279ad3..dac9ca2 100644
--- a/go/internal/gcimporter/bexport_test.go
+++ b/go/internal/gcimporter/bexport_test.go
@@ -63,7 +63,10 @@
 		if info.Files == nil {
 			continue // empty directory
 		}
-		exportdata := gcimporter.BExportData(conf.Fset, pkg)
+		exportdata, err := gcimporter.BExportData(conf.Fset, pkg)
+		if err != nil {
+			t.Fatal(err)
+		}
 
 		imports := make(map[string]*types.Package)
 		fset2 := token.NewFileSet()
@@ -306,7 +309,10 @@
 	}
 
 	// export
-	exportdata := gcimporter.BExportData(fset1, pkg)
+	exportdata, err := gcimporter.BExportData(fset1, pkg)
+	if err != nil {
+		t.Fatal(err)
+	}
 
 	// import
 	imports := make(map[string]*types.Package)