diff -r 000000000000 -r 6474c204b198 js/src/tests/js1_8_5/extensions/regress-631723.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/js1_8_5/extensions/regress-631723.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,10 @@
+// Any copyright is dedicated to the Public Domain.
+// http://creativecommons.org/licenses/publicdomain/
+
+var o = {a:1, b:2};
+o.watch("p", function() { return 13; });
+delete o.p;
+o.p = 0;
+assertEq(o.p, 13);
+
+reportCompare(0, 0, 'ok');