Being the guy who did the changes to ExtUtils::ParseXS, let me add my support for what tye said: The code in question worked purely by accident. The proper way to declare or initialize variables in an XSUB is in a PRE_INIT block! ExtUtils::ParseXS 3.XX just became strict in telling you about the problem in your code. It could have instead broken your code to segfault because of the old behaviour being an accidental misfeature and side-effect of the horrors that lurk in EU::ParseXS' code generation.