Objective-C sources

I'm making bindings to a library partially written in Objective-C. If I put those sources under c-sources, I get stuff like Warning: the following files would be used as linker inputs, but linking is not being done: glfw/lib/cocoa/cocoa_enable.m ghc: no input files How can I fix this? The problem is in the "if os(darwin)" of this project: http://github.com/bsl/GLFW-b