Error with NSNumber Category because of NSCFNumber

Question

I am using WSDL2OBJC for an OS X project. Part of the code generated by WSDL2OBJC adds a category to NSNumber. While I'm using the code I attempt to call the new method on an NSNumber and get an error:

+[NSCFNumber xmlNodeForDoc:elementName:]: unrecognized selector sent to class 0x7fff70b6b8c8

I've read that NSNumber is a class cluster and has private classes and that NSCFNumber is the class for ints. How can I get this to work? I can't add the category to NSCFNumber since it is a private class. This same code works for an iPhone project that I have.