GCC does not allow unused attribute in this position on a function definition

GCC does not allow unused attribute in this position on a function definition

I'm getting that warning from this:
static NSString *NSStringFromRCLAttribute(RCLAttribute attribute)
__attribute__((unused)) {
switch (attribute) {
case RCLAttributeRect: return @"rcl_rect";
case RCLAttributeSize: return @"rcl_size";
case RCLAttributeOrigin: return @"rcl_origin";
}
}
Is this a compiler-specific warning? How is this fixed? Is there an unused
substitute or can unused just be omitted?