Hi, I tried to submit a improvement for the Windows build but the tracker is not accessible without a login. On Windows if someone does a Debug build of an extension the flag _DEBUG is set and so the Python Interpreter sets Py_DEBUG and for all extension modules "_d" is appended to load the debug version of a module. This is not really practical because then all modules and the Python Interpreter must be build in Debug mode. For some modules this is even not possible for Windows. :-( To do a debug build for a Cython generated extension with a normal Python Interpreter (none Debug) I have to patch the pyconfig.h file and undef _DEBUG or I must patch the generated c file from Cython to undef _DEBUG before pyconfig.h or Python.h is included. (and enable it afterwards) Is it possible to add a flag to Cython to generate code that does this ? Something like described in Boost.Python: http://hepunx.rl.ac.uk/BFROOT/dist/releases/26.0.0/boost/libs/python/doc/bui... It is enough to have a new Preprocessor Flag, if set, then surround the Python.h inclusion with a disabled _DEBUG. My workarround is to disable it before pyconfig.h (Python.h) include: #ifdef _DEBUG #undef _DEBUG #define _RESTORE #endif and enable it afterwards #ifdef _RESTORE #define _DEBUG #undef _RESTORE #endif Regards, Wolfgang