Fixed by commit 62286d5869e7680741523d2a11be77cb79b83c99 Author: Karl Williamson <khw@cpan.org> Date: Fri Mar 22 11:32:32 2019 -0600 PATCH: [perl #133889] Assertion failure I did not bisect this, but this is a regression. This code is using a user-defined property that isn't defined. It should catch that and, since this is within regex sets, quit, but instead continues and ends up using an undefined value. -- Karl Williamson --- via perlbug: queue: perl5 status: open https://rt.perl.org/Ticket/Display.html?id=133889