Getting PowerMockito to mock a static method on an Interface?

I have a library I am trying to mock for testing... There is a Java 8 interface with a static method implementation like this:

public interface Router {
    public static Router router(Object param) {
        return new RouterImpl(param);
    }
}

And I am trying to mock that returned value:

PowerMockito.mockStatic(Router.class);
PowerMockito.doReturn(mockRouter).when(Router.router(any()));

But when I run the tests through a debugger, the mock instance is not returned.

I've tried a number of different permutations of the static mocking, but I cannot get the static method to return my mock value. Any thoughts?