new file mode 100644
--- /dev/null
+++ b/js/src/jit-test/tests/basic/bug613399.js
@@ -0,0 +1,3 @@
+// don't assert
+/((?=()+))?/.exec("");
+

--- a/js/src/yarr/pcre/pcre_exec.cpp
+++ b/js/src/yarr/pcre/pcre_exec.cpp
@@ -699,17 +699,17 @@ RECURSE:
                 if (stack.currentFrame->locals.number > 0) {
                     if (stack.currentFrame->locals.offset >= md.offsetMax)
                         md.offsetOverflow = true;
                     else {
                         int start = md.offsetVector[md.offsetEnd - stack.currentFrame->locals.number];
                         int end = stack.currentFrame->args.subjectPtr - md.startSubject;
                         if (start == end && stack.currentFrame->args.groupMatched) {
                             DPRINTF(("empty string while group already matched; bailing"));
-                            RRETURN;
+                            RRETURN_NO_MATCH;
                         }
                         DPRINTF(("saving; start: %d; end: %d\n", start, end));
                         JS_ASSERT(start <= end);
                         md.setOffsetPair(stack.currentFrame->locals.number, start, end);
                         if (stack.currentFrame->args.offsetTop <= stack.currentFrame->locals.offset)
                             stack.currentFrame->args.offsetTop = stack.currentFrame->locals.offset + 2;
                     }
                 }