diff --git a/src/cmd/link/internal/ld/stackcheck.go b/src/cmd/link/internal/ld/stackcheck.go
index 24a96fb..98e7eda 100644
--- a/src/cmd/link/internal/ld/stackcheck.go
+++ b/src/cmd/link/internal/ld/stackcheck.go
@@ -42,7 +42,7 @@
 
 // stackCheckIndirect is a sentinel Sym value used to represent the
 // target of an indirect/closure call.
-const stackCheckIndirect loader.Sym = -1
+const stackCheckIndirect loader.Sym = ^loader.Sym(0)
 
 // doStackCheck walks the call tree to check that there is always
 // enough stack space for call frames, especially for a chain of
diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go
index 1dea663..455ef58 100644
--- a/src/cmd/link/internal/loader/loader.go
+++ b/src/cmd/link/internal/loader/loader.go
@@ -27,7 +27,7 @@
 
 // Sym encapsulates a global symbol index, used to identify a specific
 // Go symbol. The 0-valued Sym is corresponds to an invalid symbol.
-type Sym int
+type Sym uint32
 
 // Relocs encapsulates the set of relocations on a given symbol; an
 // instance of this type is returned by the Loader Relocs() method.
@@ -364,6 +364,9 @@
 		panic("addSym called after external symbol is created")
 	}
 	i := Sym(len(l.objSyms))
+	if int(i) != len(l.objSyms) { // overflow
+		panic("too many symbols")
+	}
 	addToGlobal := func() {
 		l.objSyms = append(l.objSyms, objSym{r.objidx, li})
 	}
@@ -485,6 +488,9 @@
 // name/version.
 func (l *Loader) newExtSym(name string, ver int) Sym {
 	i := Sym(len(l.objSyms))
+	if int(i) != len(l.objSyms) { // overflow
+		panic("too many symbols")
+	}
 	if l.extStart == 0 {
 		l.extStart = i
 	}