FYI, "the stack" under an MS compiler defaults to 1MB. It's easy to experiment with different stack allocations from the cmdline, like this example: editbin /stack:2000000 python.exe The ~2MB there is enough that test_compiler runs to completion normally under a release-build Python, and under a debug-build Python. In a debug-build Windows Python, each MB allocated to the stack allows about 400 recursion levels (according to Misc/find_recursionlimit.py), and running compiler.compile() directly on test_parser.py requires more than 800 levels, so a 2MB stack must be near the insanity limit for the debug build on this test. So the easiest way to get the -uall test suite running on Windows again is to fiddle linker flags to boost the stack size. I'm not sure real apps need it. If they do and we don't "fix it", what happens is that the process mysteriously just vanishes (no error msg, nothing in the system or application event logs either) with a 128 exit code. That's a disaster. Alas, I don't have a theory for how we could be managing to screw up the OS so badly -- but then I guess you really can't spell Windows XP without Windows <0.9 wink>.