@rough-minister-58256 Yeah 'none'/None didn't work at all. Empty list "works" but it just has the same behavior as "current" as far as I can tell -- although I'm not convinced there isn't a cached wheel somewhere I need to blow away. If I find some free time I might explore the code to better understand what's going on. It's kind of a messed up situation -- these third party modules are designed to have native code "speedups" but fallback to pure python in the case where those speedups fail to compile for some reason (usually due to a missing system dep, you know, like gcc!) The only way to know that it won't work is to try it and watch it fail and fall back to the pure python module. Instead of doing that, I don't want it to ever try, because if it succeeds, it will build a binary on the wrong platform. But, unless the setup.py can be asked to not try, or unless the python can somehow be hobbled such that it has no ability to ever build extension modules, I'm not sure how to solve the problem. (The very specific problem I'm trying to solve is building linux docker containers that hold .pex files. If you build the pex on a mac you can't copy it into a linux docker container.)