I'm still trying to sort this out. Some concerns and questions: I don't like the new MatchFilename, because it triggers on *all* platforms that #define HAVE_DIRENT_H. Anyone, doesn't that trigger on straight Linux systems too (all I know is that it's part of the Single UNIX Specification)? I don't like it because it implements a woefully inefficient algorithm: it cycles through the entire directory looking for a case-sensitive match. But there can be hundreds of .py files in a directory, and on average it will need to look at half of them, while if this triggers on straight Linux there's no need to look at *any* of them there. I also don't like it because it apparently triggers on Cygwin too but the code that calls it doesn't cater to that Cygwin possibly *should* be defining ALTSEP as well as SEP. Would rather dump MatchFilename and rewrite in terms of the old check_case (which should run much quicker, and already comes in several appropriate platform-aware versions -- and I clearly minimize the chance of breakage if I stick to that time-tested code). Steven, there is a "#ifdef macintosh" version of check_case already. Will that or won't that work correctly on your variant of Mac? If not, would you please supply a version that does (along with the #ifdef'ery needed to recognize your Mac variant)? Jason, I *assume* that the existing "#if defined(MS_WIN32) || defined(__CYGWIN__)" version of check_case works already for you. Scream if that's wrong. Steven and Jack, does getenv() work on both your flavors of Mac? I want to make PYTHONCASEOK work for you too.