diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/basic/bug631219.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/basic/bug631219.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,10 @@
+// don't assert or crash
+function g(o) {
+    o.__proto__ = arguments;
+    o.length = 123;
+}
+function f() {
+    g(arguments);
+}
+f();
+