Linker Command Failed with exit code 1 Category

Question

I am trying to write a SIMBL plugin for Terminal. When attempting to add a category to TTView, I get:

Undefined symbols for architecture x86_64:
"_OBJC_CLASS_$_TTView", referenced from:
  l_OBJC_$_CATEGORY_TTView_$_MySimplePlugin in MySimplePlugin.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I have two classes, TTView and MySimplePlugin in the same files (both interfaces in a .h file and both implementations in a .m file). The interface file has TTView defined as:

@interface TTView 
@end

and the implementation is where I attempt to add a category to it:

@implementation TTView (MySimplePlugin)


@end

MySimplePlugin is the name of the file as well as the other class in the file. I am not sure where my mistake is.