Trouble with DLL address

[dnewbie]

I have a DLL which exports a function GetFunction. GetFunction 
returns a pointer to RealFunction. Now I want to run RealFunction 
from my D program, but for some reason I get the wrong address. 
Here is the code.

---- dll64.c -----
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
int __stdcall RealFunction(int a)
{
    return a + 1;
}

typedef int (__stdcall *FuncPtr)(int);

FuncPtr __stdcall GetFunction()
{
    return &RealFunction;
}

---- mydll64.def ----
LIBRARY mydll64.dll
EXPORTS
GetFunction
---------------------

build with MSVC64:
cl -c dll64.c -Fomydll64.obj
link /DLL /OUT:mydll64.dll mydll64.obj /DEF:mydll64.def

And this is the D program.

---- testdll64d.d ----
// dmd -m64 -c testdll64d.d -oftestdll64d.obj
// link /OUT:testdll64d.exe testdll64d.obj

import core.runtime;
import std.c.windows.windows;
import std.stdio;

alias extern(Windows) int function(int) FuncPtr;

int main(string[] args)
{
    HMODULE dll          = LoadLibraryA("mydll64.DLL");
    FARPROC getFunction  = GetProcAddress(dll, "GetFunction");
    FuncPtr realFunction = cast(FuncPtr) getFunction();

    writefln("dll address:          %08x", dll);
    writefln("GetFunction address:  %08x", getFunction);
    writefln("RealFunction address: %08x", realFunction);
    writefln("RealFunction result:  %d",   realFunction(7));//<-- 
CRASH

    return 0;
}
----------------------

Output:
dll address:          180000000
GetFunction address:  180001020
RealFunction address: ffffffff80001000
<CRASH>

BTW, this works:
FuncPtr realFunction = cast(FuncPtr) (getFunction() & 
0x00000000ffffffff | cast(size_t) dll);