diff --git a/core/modules/simpletest/tests/common.test b/core/modules/simpletest/tests/common.test
index 8936808..4c50806 100644
--- a/core/modules/simpletest/tests/common.test
+++ b/core/modules/simpletest/tests/common.test
@@ -733,10 +733,12 @@ class CascadingStylesheetsTestCase extends DrupalWebTestCase {
     $system_path = drupal_get_path('module', 'system');
     drupal_add_css($system_path . '/system.base.css', array('group' => CSS_SYSTEM, 'weight' => -10));
     drupal_add_css($system_path . '/system.theme.css', array('group' => CSS_SYSTEM));
+    drupal_add_css($system_path . '/system.admin.css', array('group' => CSS_SYSTEM));
 
     $expected = array(
       $system_path . '/system.base.css',
       $system_path . '/system.theme.css',
+      $system_path . '/system.admin.css',
       drupal_get_path('module', 'simpletest') . '/simpletest.css',
     );