diff --git a/modules/system/system.module b/modules/system/system.module
index 52b95b3a8d9..cdf45128802 100644
--- a/modules/system/system.module
+++ b/modules/system/system.module
@@ -296,7 +296,7 @@ function system_menu($may_cache) {
      */
     if (arg(0) == 'admin') {
       global $custom_theme;
-      $custom_theme = variable_get('admin_theme', 'bluemarine');
+      $custom_theme = variable_get('admin_theme', '0');
       drupal_add_css(drupal_get_path('module', 'system') .'/admin.css', 'core');
     }
 
@@ -417,7 +417,7 @@ function system_admin_theme_settings() {
     '#options' => $options,
     '#title' => t('Administration theme'),
     '#description' => t('Choose which theme the administration pages should display in. If you choose "System default" the administration pages theme will display in the same theme the rest of the site uses.'),
-    '#default_value' => variable_get('admin_theme', 'bluemarine'),
+    '#default_value' => variable_get('admin_theme', '0'),
   );
 
   // In order to give it our own submit, we have to give it the default submit
@@ -431,7 +431,7 @@ function system_admin_theme_settings() {
 
 function system_admin_theme_submit($form_id, $form_values) {
   // If we're changing themes, make sure the theme has its blocks initialized.
-  if ($form_values['admin_theme'] != variable_get('admin_theme', 'bluemarine')) {
+  if ($form_values['admin_theme'] != variable_get('admin_theme', '0')) {
     $result = db_query("SELECT status FROM {blocks} WHERE theme = '%s'", $form_values['admin_theme']);
     if (!db_num_rows($result)) {
       system_initialize_theme_blocks($form_values['admin_theme']);
@@ -1215,6 +1215,13 @@ function system_themes_submit($form_id, $form_values) {
         }
       }
     }
+    if (($admin_theme = variable_get('admin_theme', '0')) != '0') {
+      drupal_set_message(t('Please note that the <a href="!admin_theme_page">administration theme</a> is still set to the %admin_theme theme; consequently, the theme on this page remains unchanged. All non-administrative sections of the site, however, will show the selected %selected_theme theme by default.', array(
+        '!admin_theme_page' => url('admin/settings/admin'),
+        '%admin_theme' => $admin_theme,
+        '%selected_theme' => $values['theme_default'],
+      )));
+    }
     variable_set('theme_default', $form_values['theme_default']);
   }
   else {