Dagger does not override module as expected

I'm using Square's Dagger v1.0.1 for dependency injection and I cannot make overrides = true to work as expected.

I have a provider class for test named MyGameTestModule.java :

@Module(
        includes = { BaseModule.class, NetModule.class},
        injects = { MyGame.class, MyManager.class },
        overrides = true
)
public class MyGameTestModule {

    // ...

    @Provides
    @Singleton
    DummyInterface provideDummyInterface() {
        return new DummyInterface() {
            @Override
            public Bar getBar() {
                // return actual Bar
            }
        };
    }
}

And I have a test like this named MyManagerTest.java :

public class MyManagerTest {
    @Inject
    public MyManager myManager;

    // ...

    @Before
    public void setup() {
        ObjectGraph objectGraph = ObjectGraph.create(new TestModule());
        objectGraph.inject(this);
    }

    @Module(
        includes = {MyGameTestModule.class}, 
        injects = {MyManagerTest.class}, 
        overrides = true
    )
    public static class TestModule {
        @Provides
        @Singleton
        DummyInterface provideDummyInterface() {
            return new DummyInterface() {
                @Override
                public Bar doSomething() {
                    // return mocked Bar
                }
            };
        }
    }     
}

But when I run my tests, Dagger throws an exception like this:

java.lang.IllegalArgumentException: Duplicate: com.foo.DummyInterface com.foo.MyManagerTest$TestModule.provideDummyInterface() com.foo.DummyInterface com.foo.MyGameTestModule.provideDummyInterface() at dagger.internal.UniqueMap.put(UniqueMap.java:29) at dagger.internal.plugins.reflect.ReflectiveModuleAdapter.handleBindings(ReflectiveModuleAdapter.java:104) at dagger.internal.plugins.reflect.ReflectiveModuleAdapter.getBindings(ReflectiveModuleAdapter.java:89) at dagger.ObjectGraph$DaggerObjectGraph.makeGraph(ObjectGraph.java:174) at dagger.ObjectGraph$DaggerObjectGraph.access$000(ObjectGraph.java:132) at dagger.ObjectGraph.create(ObjectGraph.java:129) at com.foo.MyManagerTest.setup(MyManagerTest.java:38)

Am I missing something? Isn't it supposed to override DummyInterface in MyGameTestModule with "overrides = true" provided to Module?

Thanks in advance.