diff --git a/misc/cgo/testshared/src/depBase/dep.go b/misc/cgo/testshared/src/depBase/dep.go
index c3ae96fe98..a518b4efe2 100644
--- a/misc/cgo/testshared/src/depBase/dep.go
+++ b/misc/cgo/testshared/src/depBase/dep.go
@@ -1,5 +1,10 @@
 package depBase
 
+import (
+	"os"
+	"reflect"
+)
+
 var V int = 1
 
 var HasMask []string = []string{"hi"}
@@ -13,6 +18,10 @@ type Dep struct {
 }
 
 func (d *Dep) Method() int {
+	// This code below causes various go.itab.* symbols to be generated in
+	// the shared library. Similar code in ../exe/exe.go results in
+	// exercising https://github.com/golang/go/issues/17594
+	reflect.TypeOf(os.Stdout).Elem()
 	return 10
 }
 
diff --git a/misc/cgo/testshared/src/exe/exe.go b/misc/cgo/testshared/src/exe/exe.go
index 136803fbc1..31fbedd31c 100644
--- a/misc/cgo/testshared/src/exe/exe.go
+++ b/misc/cgo/testshared/src/exe/exe.go
@@ -2,11 +2,17 @@ package main
 
 import (
 	"depBase"
+	"os"
+	"reflect"
 	"runtime"
 )
 
 func main() {
 	defer depBase.ImplementedInAsm()
+	// This code below causes various go.itab.* symbols to be generated in
+	// the executable. Similar code in ../depBase/dep.go results in
+	// exercising https://github.com/golang/go/issues/17594
+	reflect.TypeOf(os.Stdout).Elem()
 	runtime.GC()
 	depBase.V = depBase.F() + 1
 }
diff --git a/src/cmd/compile/internal/gc/reflect.go b/src/cmd/compile/internal/gc/reflect.go
index da63f87c22..57192dec1c 100644
--- a/src/cmd/compile/internal/gc/reflect.go
+++ b/src/cmd/compile/internal/gc/reflect.go
@@ -1395,11 +1395,11 @@ func dumptypestructs() {
 		o += len(imethods(i.itype)) * Widthptr // skip fun method pointers
 		// at runtime the itab will contain pointers to types, other itabs and
 		// method functions. None are allocated on heap, so we can use obj.NOPTR.
-		ggloblsym(i.sym, int32(o), int16(obj.DUPOK|obj.NOPTR))
+		ggloblsym(i.sym, int32(o), int16(obj.DUPOK|obj.NOPTR|obj.LOCAL))
 
 		ilink := Pkglookup(i.t.tconv(FmtLeft)+","+i.itype.tconv(FmtLeft), itablinkpkg)
 		dsymptr(ilink, 0, i.sym, 0)
-		ggloblsym(ilink, int32(Widthptr), int16(obj.DUPOK|obj.RODATA))
+		ggloblsym(ilink, int32(Widthptr), int16(obj.DUPOK|obj.RODATA|obj.LOCAL))
 	}
 
 	// process ptabs
diff --git a/src/runtime/iface.go b/src/runtime/iface.go
index b55a9ed893..f7ad40d1c0 100644
--- a/src/runtime/iface.go
+++ b/src/runtime/iface.go
@@ -138,6 +138,10 @@ func additab(m *itab, locked, canfail bool) {
 		throw("invalid itab locking")
 	}
 	h := itabhash(inter, typ)
+	if m == hash[h] {
+		println("duplicate itab for", typ.string(), "and", inter.typ.string())
+		throw("duplicate itabs")
+	}
 	m.link = hash[h]
 	atomicstorep(unsafe.Pointer(&hash[h]), unsafe.Pointer(m))
 }