no size for type nothrow extern (Windows) int()

[cal]

I want to call Windows api function VirtualAlloc. I include 
std.c.windows.windows but get the following error from dmd 2.061 
(and 2.060):

Error: no size for type nothrow extern (Windows) int()

What does this message mean? If I provide my own prototype of the 
function, same error.