diff --git a/src/go/types/infer.go b/src/go/types/infer.go
index 405657c84f..06e52c0c34 100644
--- a/src/go/types/infer.go
+++ b/src/go/types/infer.go
@@ -73,9 +73,11 @@ func (check *Checker) infer(pos token.Pos, tparams []*TypeName, params *Tuple, a
 		// infer an untyped nil type as type parameter type. Ignore untyped
 		// nil by making sure all default argument types are typed.
 		if isTyped(targ) && !check.identical0(par.typ, targ, true, nil, targs) {
-			check.errorf(arg.pos(), "default type %s for %s does not match %s = %s",
-				Default(arg.typ), arg.expr, par.typ, check.subst(pos, par.typ, tparams, targs),
-			)
+			// TODO(gri) see TODO comment above
+			// check.errorf(arg.pos(), "default type %s for %s does not match %s = %s",
+			// 	Default(arg.typ), arg.expr, par.typ, check.subst(pos, par.typ, tparams, targs),
+			// )
+			check.errorf(arg.pos(), "default type %s for %s does not match %s", Default(arg.typ), arg.expr, par.typ)
 			return nil
 		}
 	}
diff --git a/src/go/types/lookup.go b/src/go/types/lookup.go
index ab21d04c00..d30cb41f32 100644
--- a/src/go/types/lookup.go
+++ b/src/go/types/lookup.go
@@ -362,14 +362,14 @@ func (check *Checker) missingMethod(V Type, T *Interface, static bool) (method,
 		// does not instantiate the methods).
 		// In order to compare the signatures, substitute the receiver
 		// type parameters of ftyp with V's instantiation type arguments.
-		// This lazily instantiates the method f.
-		if Vn != nil {
+		// This lazily instantiates the signature of method f.
+		if Vn != nil && len(Vn.targs) > 0 {
 			ftyp = check.subst(token.NoPos, ftyp, ftyp.rparams, Vn.targs).(*Signature)
 		}
 
 		// If the methods have type parameters we don't care whether they
 		// are the same or not, as long as they match up. Use inference
-		// comparison in that case.
+		// comparison (provide non-nil tparams to identical0) in that case.
 		// TODO(gri) is this always correct? what about type bounds?
 		// (Alternative is to rename/subst type parameters and compare.)
 		var tparams []Type