diff --git a/src/cmd/compile/internal/types2/types_test.go b/src/cmd/compile/internal/types2/types_test.go
index 11dca0b53d..1525844f2d 100644
--- a/src/cmd/compile/internal/types2/types_test.go
+++ b/src/cmd/compile/internal/types2/types_test.go
@@ -7,3 +7,6 @@ package types2
 func init() {
 	acceptMethodTypeParams = true
 }
+
+// Debug is set if types2 is built with debug mode enabled.
+const Debug = debug
diff --git a/src/cmd/compile/internal/types2/typestring.go b/src/cmd/compile/internal/types2/typestring.go
index 40016697b7..e85cc8ed35 100644
--- a/src/cmd/compile/internal/types2/typestring.go
+++ b/src/cmd/compile/internal/types2/typestring.go
@@ -226,7 +226,7 @@ func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
 				empty = false
 			}
 		}
-		if t.allMethods == nil || len(t.methods) > len(t.allMethods) {
+		if debug && (t.allMethods == nil || len(t.methods) > len(t.allMethods)) {
 			if !empty {
 				buf.WriteByte(' ')
 			}
diff --git a/src/cmd/compile/internal/types2/typestring_test.go b/src/cmd/compile/internal/types2/typestring_test.go
index d98e9a5ade..618fdc0757 100644
--- a/src/cmd/compile/internal/types2/typestring_test.go
+++ b/src/cmd/compile/internal/types2/typestring_test.go
@@ -138,6 +138,10 @@ func TestTypeString(t *testing.T) {
 var nopos syntax.Pos
 
 func TestIncompleteInterfaces(t *testing.T) {
+	if !Debug {
+		t.Skip("requires type checker to be compiled with debug = true")
+	}
+
 	sig := NewSignature(nil, nil, nil, false)
 	m := NewFunc(nopos, nil, "m", sig)
 	for _, test := range []struct {