Oh, it's even worse: "./python -m test test_sys" is enough to reproduce the crash. It looks like the crashs was introduced by the following change which (indirectly) adds one more Python frame in the code to execute test_sys. changeset: 98417:281ab7954d7c user: Victor Stinner <victor.stinner@gmail.com> date: Tue Sep 29 23:36:27 2015 +0200 files: Lib/test/libregrtest/main.py description: Issue #25220: Enhance regrtest --coverage Add a new Regrtest.run_test() method to ensure that --coverage pass the same options to the runtest() function.