1 files changed, 3 insertions, 0 deletions
diff --git a/op.c b/op.c
index af7ec8bec2..75d7583b18 100644
--- a/op.c
+++ b/op.c
@@ -3232,6 +3232,9 @@ OP *block;
 		SAVEFREESV(compcv);
 		goto done;
 	    }
+	    /* ahem, death to those who redefine active sort subs */
+	    if (curstack == sortstack && sortcop == CvSTART(cv))
+		croak("Can't redefine active sort subroutine %s", name);
 	    const_sv = cv_const_sv(cv);
 	    if (const_sv || dowarn) {
 		line_t oldline = curcop->cop_line;