diff --git a/core/includes/common.inc b/core/includes/common.inc
index 6c489b2..a86a690 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -4225,6 +4225,14 @@ function drupal_pre_render_scripts($elements) {
       $element = $element_defaults;
       $element['#attributes']['src'] = file_create_url($group['data']);
       $element['#browsers'] = $group['browsers'];
+
+      if (!empty($group['async'])) {
+        $element['#attributes']['async'] = 'async';
+      }
+      if (!empty($group['defer'])) {
+        $element['#attributes']['defer'] = 'defer';
+      }
+
       $elements[] = $element;
     }
     // For non-file types, and non-aggregated files, add a script element per
@@ -4293,11 +4301,6 @@ function drupal_pre_render_scripts($elements) {
  * if their 'preprocess' flag is TRUE. Items of the 'inline', 'settings', or
  * 'external' type are not groupable.
  *
- * This function also ensures that the process of grouping items does not change
- * their relative order. This requirement may result in multiple groups for the
- * same type and browsers, if needed to accommodate other items in
- * between.
- *
  * @param $javascript
  *   An array of JavaScript items, as returned by drupal_add_js(), but after
  *   alteration performed by drupal_get_js().
@@ -4315,48 +4318,47 @@ function drupal_group_js($javascript) {
   $groups = array();
   // If a group can contain multiple items, we track the information that must
   // be the same for each item in the group, so that when we iterate the next
-  // item, we can determine if it can be put into the current group, or if a
-  // new group needs to be made for it.
-  $current_group_keys = NULL;
-  $index = -1;
+  // item, we can determine if it can be put into an existing group.
+  $index = FALSE;
   foreach ($javascript as $item) {
-    // The browsers for which the JavaScript item needs to be loaded is part of
-    // the information that determines when a new group is needed, but the order
-    // of keys in the array doesn't matter, and we don't want a new group if all
-    // that's different is that order.
-    ksort($item['browsers']);
-
     switch ($item['type']) {
       case 'file':
         // Group file items if their 'preprocess' flag is TRUE.
-        // Help ensure maximum reuse of aggregate files by only grouping
-        // together items that share the same 'group' value and 'every_page'
-        // flag. See drupal_add_js() for details about that.
-        $group_keys = $item['preprocess'] ? array($item['type'], $item['group'], $item['every_page'], $item['browsers']) : FALSE;
+        if ($item['preprocess']) {
+          $group_keys = array(
+            $item['type'],
+            $item['group'],
+            $item['every_page'],
+            $item['browsers'],
+            $item['async'],
+            $item['defer'],
+          );
+          $index = md5(serialize($group_keys));
+        }
+        else {
+          $index = FALSE;
+        }
         break;
 
       case 'external':
       case 'setting':
       case 'inline':
         // Do not group external, settings, and inline items.
-        $group_keys = FALSE;
+        $index = FALSE;
         break;
     }
 
-    // If the group keys don't match the most recent group we're working with,
-    // then a new group must be made.
-    if ($group_keys !== $current_group_keys) {
-      $index++;
+    // If the group index is new, then create a new group.
+    if (!isset($groups[$index])) {
       // Initialize the new group with the same properties as the first item
       // being placed into it. The item's 'data' and 'weight' properties are
       // unique to the item and should not be carried over to the group.
       $groups[$index] = $item;
       unset($groups[$index]['data'], $groups[$index]['weight']);
       $groups[$index]['items'] = array();
-      $current_group_keys = $group_keys ? $group_keys : NULL;
     }
 
-    // Add the item to the current group.
+    // Add the item to its group.
     $groups[$index]['items'][] = $item;
   }