diff -r 000000000000 -r 6474c204b198 js/src/tests/js1_8_5/extensions/regress-637985.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/js1_8_5/extensions/regress-637985.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,8 @@
+// Any copyright is dedicated to the Public Domain.
+// http://creativecommons.org/licenses/publicdomain/
+
+var obj = {};
+obj.watch(-1, function(){});
+obj.unwatch("-1");  // don't assert
+
+reportCompare(0, 0, 'ok');
\ No newline at end of file