diff --git a/src/cmd/compile/internal/gc/go.go b/src/cmd/compile/internal/gc/go.go
index 21a8a68..024810e 100644
--- a/src/cmd/compile/internal/gc/go.go
+++ b/src/cmd/compile/internal/gc/go.go
@@ -98,6 +98,9 @@
 func (v Val) Ctype() int {
 	switch x := v.U.(type) {
 	default:
+		Fatal("unexpected Ctype for %T", v.U)
+		panic("not reached")
+	case nil:
 		return 0
 	case *NilVal:
 		return CTNIL