--- a/js/src/jsxml.cpp
+++ b/js/src/jsxml.cpp
@@ -6358,17 +6358,17 @@ xml_replace(JSContext *cx, uintN argc, j
     }
 
     xml = CHECK_COPY_ON_WRITE(cx, xml, obj);
     if (!xml)
         return JS_FALSE;
 
     bool haveIndex;
     if (argc == 0) {
-        haveIndex = true;
+        haveIndex = false;
     } else {
         if (!js_IdValIsIndex(cx, vp[2], &index, &haveIndex))
             return JS_FALSE;
     }
 
     if (!haveIndex) {
         /*
          * Call function QName per spec, not ToXMLName, to avoid attribute

--- a/js/src/tests/e4x/XML/jstests.list
+++ b/js/src/tests/e4x/XML/jstests.list
@@ -48,8 +48,9 @@ script 13.4.4.7.js
 script 13.4.4.8.js
 script 13.4.4.9.js
 script regress-291930.js
 script regress-324422-1.js
 skip script regress-324422-2.js # slow
 skip script regress-324688.js # bug 528404 - disable due to random timeouts
 script regress-336921.js
 script regress-376773.js
+script regress-621464.js

new file mode 100644
--- /dev/null
+++ b/js/src/tests/e4x/XML/regress-621464.js
@@ -0,0 +1,51 @@
+/* -*- Mode: java; tab-width:8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is JavaScript Engine testing utilities.
+ *
+ * The Initial Developer of the Original Code is
+ * Mozilla Foundation.
+ * Portions created by the Initial Developer are Copyright (C) 2007
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s): Andrew Drake
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+
+var BUGNUMBER = 621464;
+var summary = '<x>a</x>.replace() == <x>a</x>';
+
+printBugNumber(BUGNUMBER);
+START(summary);
+
+var expected = <x>a</x>;
+var actual = <x>a</x>.replace();
+
+TEST(0, expected, actual);
+
+END();