I am trying to modify a program using SIMBL. I am swapping methods and I have the class IMWindowController categorized with the new implementation of the method. When I build the bundle I get this linker error: Code: "_OBJC_CLASS_$_IMWindowController", referenced from: l_OBJC_$_CATEGORY_IMWindowController_$_Injected in MyInjector.o objc-class-ref-to-IMWindowController in MyInjector.o ld: symbol(s) not found I google this type of errors and I figuered out that I need to some binary, but I don't know: 1. Which binary 2. And how to link that binary If someone could point me in the right direction, it would be great. Thanks.