Hi Martin,

It was nice meeting you at Pycon.

I finally took the time to set up a windows 64 bits environment, and here are the exact steps I needed to do to reproduce the issue, and fix it by hand:

  - Start fresh from windows 7 64 bits
  - clone python hg repository, and checkout the 2.6 branch (path referred as $PYTHON_ROOT from now on).
  - build python with VS 2008 pro, 64 bits (release mode)
  - install mingw-w64. I used this exact version: mingw-w64-1.0-bin_i686-mingw_20110328.zip (release 1.0, targetting win64 but running in 32 bits native mode), and unzipped it in C:¥
  - I compiled a trivial C extension in foo.c as follows:

C:\mingw-w64\bin\x86_64-w64-mingw32-gcc.exe foo.c -I $PYTHON_ROOT\Include -I $PYTHON_ROOT\PC -shared -o foo.pyd  $PYTHON_ROOT\PCbuild\amd64\python26.lib -DMS_WIN64

The patch removes the need for defining MS_WIN64. I don't know exactly the policies for which branch this could be applied - anything below 2.6 does not make much sense since most win64 users use 2.6 at least. Ideally, it could be backported to 2.6, 2.7 and 3.1 ?