diff -r 000000000000 -r 6474c204b198 js/src/tests/ecma_5/RegExp/regress-613820-3.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/ecma_5/RegExp/regress-613820-3.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,9 @@
+/* Capture group reset to undefined during second iteration, so backreference doesn't see prior result. */
+var re = /(?:^(a)|\1(a)|(ab)){2}/;
+var str = 'aab';
+var actual = re.exec(str);
+var expected = makeExpectedMatch(['aa', undefined, 'a', undefined], 0, str);
+checkRegExpMatch(actual, expected);
+
+if (typeof reportCompare === 'function')
+    reportCompare(true, true);