diff -r 000000000000 -r 6474c204b198 js/src/tests/js1_7/regress/regress-420399.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/js1_7/regress/regress-420399.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,37 @@
+// |reftest| skip -- obsolete test
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//-----------------------------------------------------------------------------
+var BUGNUMBER = 420399;
+var summary = 'Let expression error involving undefined';
+var actual = '';
+var expect = '';
+
+
+//-----------------------------------------------------------------------------
+test();
+//-----------------------------------------------------------------------------
+
+function test()
+{
+  enterFunc ('test');
+  printBugNumber(BUGNUMBER);
+  printStatus (summary);
+ 
+  expect = /TypeError: \(let \(a = undefined\) a\) (is undefined|has no properties)/;
+  try
+  {
+    (let (a=undefined) a).b = 3;
+  }
+  catch(ex)
+  {
+    actual = ex + '';
+  }
+
+  reportMatch(expect, actual, summary);
+
+  exitFunc ('test');
+}