diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/bug767273.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/bug767273.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,7 @@
+var prox = Proxy.create({
+  getPropertyDescriptor: function() { return undefined; },
+  has:                   function() { return true; },
+});
+
+// Don't crash.
+newGlobal().__lookupSetter__.call(prox, "e");