On Thu, 05 Jan 2017 14:22:30 -0800, jkeenan wrote: > I can confirm that 986a805c4b258067b82c4f1254518e53cdb1acdf > is the problematic commit. I took a quick look through, and the manipulation of PL_check[] looked thread-unsafe; checking a bit further I find in perlvars.h: For thread safety, modules should not write directly to this array. Instead, use the function L</wrap_op_checker>. I don't see mention of a function to remove the inserted checker again though, I guess that's rather harder to do safely. Hugo --- via perlbug: queue: perl5 status: open https://rt.perl.org/Ticket/Display.html?id=125685