Oops, it's my fault! PR 15415 fix the crash. The regression was introduced by: commit 74f6568bbd3e70806ea3219e8bacb386ad802ccf Author: Victor Stinner <vstinner@redhat.com> Date: Fri Mar 15 15:08:05 2019 +0100 bpo-36301: Add _PyWstrList structure (GH-12343) Simplified change: - static wchar_t *empty_argv[1] = {L""}; + wchar_t* empty_argv[1] = {L""}; It's a deliberate change to not waste memory: PySys_SetArgvEx() (make_sys_argv()) is only called once, whereas static keeps the memory for the whole lifecycle of the process. But I didn't notice a subtle issue with memory allocated on the stack: the code works well with gcc -O0! The bug only triggers with gcc -O3.