DEFINE_FWD_FUNC_PTR Not working

[ettorhake]

hello Jack and thank you for your excellent work. I'm trying to implement one of my programs in shellcode with your solution.
But I have a problem, I want to import this RtlCreateUserThread function from Ntdll.dll like that:

DEFINE_FWD_FUNC_PTR("Ntdll.dll", "RtlCreateUserThread", CreateUserThread);

But the program returns "CreateUserThread" is not defined, do you have a solution?

Thanks