Before v5.18.0, this'd just die() during a regex compilation. It was either exposed or caused by the following commit: 31c15ce5372b770c3ca899df6cf102f1ed6866ba is the first bad commit commit 31c15ce5372b770c3ca899df6cf102f1ed6866ba Author: Karl Williamson <public@khwilliamson.com> Date: Sat Sep 15 12:27:22 2012 -0600 PATCH: [perl #82954] Make "Can't do {n,m} with n > m into warning This commit now causes this situation to warn instead of dying. The portion of the regular expression that can't match is optimized into an OPFAIL.