SetWindowLongPtr and /Wp64

Help, readers.

#include <windows.h>
void main() {
  LONG_PTR x = 0;
  SetWindowLongPtr(0, 0, x);
}

Ok, forget the fact that the above code doesn't do anything useful. But you'd expect it to compile without a warning, right? Well, compile it with the default Visual C++ options /Wp64 at a warning level of 4 and you're treated to the following:

cl -c -Wp64 -W4 test.cpp
warning C4244: 'argument' : conversion from 'LONG_PTR' to 'LONG', possible loss of data

I couldn't figure out why SetWindowLongPtr wouldn't actually take a LONG_PTR. Based on this warning it appears to take a LONG.

So I had a peek at the WINUSER.H header file at the actual function declaration. Turns out that there's two definitions, depending on whether a preprocessor switch (_WIN64) is defined. I'll summarize:

#ifdef _WIN64
LONG_PTR SetWindowLongPtr(
    HWND hWnd,
    int nIndex,
    LONG_PTR dwNewLong
);
#else
#define SetWindowLongPtr SetWindowLong
#endif

I searched all the header files in Visual Studio to see if any of them actually define _WIN64, but none do, so I'm assuming this is something defined at compile time by a 64 bit compiler.

Is it just me, or are the header files somewhat broken in VS.NET 2003? The /Wp64 switch is supposed to spit out warnings if you're doing stuff that would cause you trouble with a 64 bit compiler. But calling SetWindowLongPtr is the right thing to do for 64-bit compatibility.

Anybody else run into this? Did you just give up and turn off the /Wp64 switch, or did you find a cleaner workaround? Or am I just doing something really stupid?