What does the declaration look like? Does it contain these _In_, etc, pieces?
I am very wary of getting clever with macro's, since what happens with:
#define MYINT int
void doSomething( MYINT foo );
or the somewhat more obscure:
void doSomethingElse( MYMACRO MYINT foo );
experience indicates that if it can be made to compile, someone is relying on it.