Hi, Looks like regcomp() doesn't detect invalid backreferences on -CURRENT, though it works normally on 6.3-RELEASE. simple testcase: 6.3-RELEASE: $ echo test | sed 's/test/\1/' sed: 1: "s/test/\1/": \1 not defined in the RE -CURRENT: $ echo test | sed 's/test/\1/' Segmentation fault (core dumped) Yuri