Support feedback: The Inspection "Non-serializable parameter type or return type of service method" under Google Web Toolkit issues is too aggressive and does the wrong thing to interfaces if you apply it's suggestion. 1. I have a GWT RPC method that returns an interface. This interface does not implement IsSerializable itself but some of the concrete implementations of this class do, the ones I want to send via RPC. The inspection warns me about this and I'd appreciate it if it had an option to not warn me for interfaces. 2. If you do let the inspection apply it's suggestion to an interface type it adds "implements IsSerializable" when for interfaces you should "extend IsSerializable".