diff --git a/js/src/jsarray.cpp b/js/src/jsarray.cpp
index 3d3e988a56e..9e1f7216786 100644
--- a/js/src/jsarray.cpp
+++ b/js/src/jsarray.cpp
@@ -1582,10 +1582,15 @@ js::array_sort(JSContext *cx, unsigned argc, Value *vp)
             allInts = allInts && v.isInt32();
         }
 
+
+        /*
+         * If the array only contains holes, we're done.  But if it contains
+         * undefs, those must be sorted to the front of the array.
+         */
         n = vec.length();
-        if (n == 0) {
+        if (n == 0 && undefs == 0) {
             args.rval().setObject(*obj);
-            return true; /* The array has only holes and undefs. */
+            return true;
         }
 
         /* Here len == n + undefs + number_of_holes. */
diff --git a/js/src/tests/ecma_5/Array/sort-array-with-holes-and-undefined.js b/js/src/tests/ecma_5/Array/sort-array-with-holes-and-undefined.js
new file mode 100644
index 00000000000..b77c6d3411f
--- /dev/null
+++ b/js/src/tests/ecma_5/Array/sort-array-with-holes-and-undefined.js
@@ -0,0 +1,32 @@
+/*
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/licenses/publicdomain/
+ */
+
+//-----------------------------------------------------------------------------
+var BUGNUMBER = 664528;
+var summary =
+  "Sorting an array containing only holes and |undefined| should move all " +
+  "|undefined| to the start of the array";
+
+print(BUGNUMBER + ": " + summary);
+
+/**************
+ * BEGIN TEST *
+ **************/
+
+var a = [, , , undefined];
+a.sort();
+
+assertEq(a.hasOwnProperty(0), true);
+assertEq(a[0], undefined);
+assertEq(a.hasOwnProperty(1), false);
+assertEq(a.hasOwnProperty(2), false);
+assertEq(a.hasOwnProperty(3), false);
+
+/******************************************************************************/
+
+if (typeof reportCompare === "function")
+  reportCompare(true, true);
+
+print("Tests complete");