I already mentioned needing .hi (I may have said hsc, whoops; Haskell Interface files) from dependencies; you really want to turn that part on, at least. And possibly ensure your other options are compatible with existing .hi files, so they can be loaded directly. I think the .o isn't used until link time, which should be irrelevant for you; but you really do want those .hi files, otherwise it must compile the dependency module to generate one.