diff --git a/core/includes/common.inc b/core/includes/common.inc
index 52a3a43..247f7ec 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -3469,68 +3469,31 @@ function drupal_pre_render_styles($elements) {
  *   The URI of the CSS cache file, or FALSE if the file could not be saved.
  */
 function drupal_build_css_cache($css) {
-  $data = '';
-  $uri = '';
-  $map = variable_get('drupal_css_cache_files', array());
-  $key = hash('sha256', serialize($css));
-  if (isset($map[$key])) {
-    $uri = $map[$key];
-  }
-
-  if (empty($uri) || !file_exists($uri)) {
-    // Build aggregate CSS file.
-    foreach ($css as $stylesheet) {
-      // Only 'file' stylesheets can be aggregated.
-      if ($stylesheet['type'] == 'file') {
-        $contents = drupal_load_stylesheet($stylesheet['data'], TRUE);
-
-        // Build the base URL of this CSS file: start with the full URL.
-        $css_base_url = file_create_url($stylesheet['data']);
-        // Move to the parent.
-        $css_base_url = substr($css_base_url, 0, strrpos($css_base_url, '/'));
-        // Simplify to a relative URL if the stylesheet URL starts with the
-        // base URL of the website.
-        if (substr($css_base_url, 0, strlen($GLOBALS['base_root'])) == $GLOBALS['base_root']) {
-          $css_base_url = substr($css_base_url, strlen($GLOBALS['base_root']));
-        }
-
-        _drupal_build_css_path(NULL, $css_base_url . '/');
-        // Anchor all paths in the CSS with its base URL, ignoring external and absolute paths.
-        $data .= preg_replace_callback('/url\(\s*[\'"]?(?![a-z]+:|\/+)([^\'")]+)[\'"]?\s*\)/i', '_drupal_build_css_path', $contents);
-      }
-    }
-
-    // Per the W3C specification at http://www.w3.org/TR/REC-CSS2/cascade.html#at-import,
-    // @import rules must proceed any other style, so we move those to the top.
-    $regexp = '/@import[^;]+;/i';
-    preg_match_all($regexp, $data, $matches);
-    $data = preg_replace($regexp, '', $data);
-    $data = implode('', $matches[0]) . $data;
+  return drupal_return_css_path($css);
+}
 
-    // Prefix filename to prevent blocking by firewalls which reject files
-    // starting with "ad*".
-    $filename = 'css_' . drupal_hash_base64($data) . '.css';
-    // Create the css/ within the files folder.
-    $csspath = 'public://css';
-    $uri = $csspath . '/' . $filename;
-    // Create the CSS file.
-    file_prepare_directory($csspath, FILE_CREATE_DIRECTORY);
-    if (!file_exists($uri) && !file_unmanaged_save_data($data, $uri, FILE_EXISTS_REPLACE)) {
-      return FALSE;
-    }
-    // If CSS gzip compression is enabled, clean URLs are enabled (which means
-    // that rewrite rules are working) and the zlib extension is available then
-    // create a gzipped version of this file. This file is served conditionally
-    // to browsers that accept gzip using .htaccess rules.
-    if (variable_get('css_gzip_compression', TRUE) && variable_get('clean_url', 0) && extension_loaded('zlib')) {
-      if (!file_exists($uri . '.gz') && !file_unmanaged_save_data(gzencode($data, 9, FORCE_GZIP), $uri . '.gz', FILE_EXISTS_REPLACE)) {
-        return FALSE;
+/**
+ * Return a uri for the given css paths.
+ */
+function drupal_return_css_path($css) {
+  $css_base_path = 'sites/default/files/css/';
+  $directories = array();
+  foreach ($css as $stylesheet) {
+    // Only 'file' stylesheets can be aggregated.
+    if ($stylesheet['type'] == 'file') {
+      $directory = str_replace('/', ';', dirname($stylesheet['data']));
+      $filename = basename($stylesheet['data']);
+      if (!isset($directories[$directory])) {
+        $directories[$directory] = array();
       }
+      $directories[$directory][] = substr($filename, 0, -4);
     }
-    // Save the updated map.
-    $map[$key] = $uri;
-    variable_set('drupal_css_cache_files', $map);
   }
+  $css_paths = array();
+  foreach ($directories as $directory => $files) {
+    $css_paths[] = $directory . '=' . implode('~', $files);
+  }
+  $uri = $css_base_path . implode(',', $css_paths) . '.css';
   return $uri;
 }
 
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 07eacd2..3745dbd 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -546,9 +546,75 @@ function system_element_info() {
 }
 
 /**
+ * Aggregate and serve css files imagecache style.
+ */
+function system_aggregate_css($css_paths_string) {
+  $css = array();
+  foreach (explode(',', substr($css_paths_string, 0, -4)) as $directory_string) {
+    list($directory, $files_string) = explode('=', $directory_string);
+    foreach (explode('~', $files_string) as $css_file) {
+      $css[] = str_replace(';', '/', $directory) . '/' . $css_file . '.css';
+    }
+  }
+
+  $data = '';
+  $uri = '';
+  foreach ($css as $stylesheet) {
+    $contents = drupal_load_stylesheet($stylesheet, TRUE);
+    // Build the base URL of this CSS file: start with the full URL.
+    $css_base_url = file_create_url($stylesheet);
+    // Move to the parent.
+    $css_base_url = substr($css_base_url, 0, strrpos($css_base_url, '/'));
+    // Simplify to a relative URL if the stylesheet URL starts with the
+    // base URL of the website.
+    if (substr($css_base_url, 0, strlen($GLOBALS['base_root'])) == $GLOBALS['base_root']) {
+      $css_base_url = substr($css_base_url, strlen($GLOBALS['base_root']));
+    }
+
+    _drupal_build_css_path(NULL, $css_base_url . '/');
+    // Anchor all paths in the CSS with its base URL, ignoring external and absolute paths.
+    $data .= preg_replace_callback('/url\(\s*[\'"]?(?![a-z]+:|\/+)([^\'")]+)[\'"]?\s*\)/i', '_drupal_build_css_path', $contents);
+  }
+
+  // Per the W3C specification at http://www.w3.org/TR/REC-CSS2/cascade.html#at-import,
+  // @import rules must proceed any other style, so we move those to the top.
+  $regexp = '/@import[^;]+;/i';
+  preg_match_all($regexp, $data, $matches);
+  $data = preg_replace($regexp, '', $data);
+  $data = implode('', $matches[0]) . $data;
+
+  $filename = $css_paths_string;
+  // Create the css/ within the files folder.
+  $csspath = 'public://css';
+  $uri = $csspath . '/' . $filename;
+  // Create the CSS file.
+  file_prepare_directory($csspath, FILE_CREATE_DIRECTORY);
+  if (!file_unmanaged_save_data($data, $uri, FILE_EXISTS_REPLACE)) {
+    return FALSE;
+  }
+  // If CSS gzip compression is enabled, clean URLs are enabled (which means
+  // that rewrite rules are working) and the zlib extension is available then
+  // create a gzipped version of this file. This file is served conditionally
+  // to browsers that accept gzip using .htaccess rules.
+  if (variable_get('css_gzip_compression', TRUE) && variable_get('clean_url', 0) && extension_loaded('zlib')) {
+    if (!file_unmanaged_save_data(gzencode($data, 9, FORCE_GZIP), $uri . '.gz', FILE_EXISTS_REPLACE)) {
+      return FALSE;
+    }
+  }
+  file_transfer($uri, array('Content-Type' => 'text/css', 'Content-Length' => strlen($data)));
+}
+
+/**
  * Implements hook_menu().
  */
 function system_menu() {
+  $items['sites/default/files/css/%'] = array(
+    'title' => 'Download aggregated css',
+    'page callback' => 'system_aggregate_css',
+    'page arguments' => array(4),
+    'access callback' => TRUE,
+    'type' => MENU_CALLBACK,
+  );
   $items['system/files'] = array(
     'title' => 'File download',
     'page callback' => 'file_download',