--- a/js/src/jsinterp.cpp
+++ b/js/src/jsinterp.cpp
@@ -1097,16 +1097,18 @@ StrictlyEqual(JSContext *cx, const Value
     Value lval = lref, rval = rref;
     if (SameType(lval, rval)) {
         if (lval.isString())
             return js_EqualStrings(lval.toString(), rval.toString());
         if (lval.isDouble())
             return JSDOUBLE_COMPARE(lval.toDouble(), ==, rval.toDouble(), JS_FALSE);
         if (lval.isObject())
             return EqualObjects(cx, &lval.toObject(), &rval.toObject());
+        if (lval.isUndefined())
+                return true;
         return lval.payloadAsRawUint32() == rval.payloadAsRawUint32();
     }
 
     if (lval.isDouble() && rval.isInt32()) {
         double ld = lval.toDouble();
         double rd = rval.toInt32();
         return JSDOUBLE_COMPARE(ld, ==, rd, JS_FALSE);
     }