Index: modules/system/system.admin.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.admin.inc,v
retrieving revision 1.309
diff -u -p -r1.309 system.admin.inc
--- modules/system/system.admin.inc	24 Sep 2010 21:36:22 -0000	1.309
+++ modules/system/system.admin.inc	27 Sep 2010 19:08:42 -0000
@@ -210,7 +210,9 @@ function system_themes_page() {
     if (!empty($theme->info['hidden'])) {
       continue;
     }
-    $admin_theme_options[$theme->name] = $theme->info['name'];
+    if (isset($theme->info['type']) && $theme->info['type'] === 'admin-theme') {
+      $admin_theme_options[$theme->name] = $theme->info['name'];
+    }
     $theme->is_default = ($theme->name == $theme_default);
 
     // Identify theme screenshot.
@@ -264,12 +266,14 @@ function system_themes_page() {
             'query' => $query,
             'attributes' => array('title' => t('Disable !theme theme', array('!theme' => $theme->info['name']))),
           );
-          $theme->operations[] = array(
-            'title' => t('Set default'),
-            'href' => 'admin/appearance/default',
-            'query' => $query,
-            'attributes' => array('title' => t('Set !theme as default theme', array('!theme' => $theme->info['name']))),
-          );
+          if(empty($theme->info['type']) || !($theme->info['type'] === 'admin-theme')) {
+            $theme->operations[] = array(
+              'title' => t('Set default'),
+              'href' => 'admin/appearance/default',
+              'query' => $query,
+              'attributes' => array('title' => t('Set !theme as default theme', array('!theme' => $theme->info['name']))),
+            );
+          }
         }
       }
       else {
Index: themes/seven/seven.info
===================================================================
RCS file: /cvs/drupal/drupal/themes/seven/seven.info,v
retrieving revision 1.5
diff -u -p -r1.5 seven.info
--- themes/seven/seven.info	14 Jan 2010 06:47:54 -0000	1.5
+++ themes/seven/seven.info	27 Sep 2010 19:08:42 -0000
@@ -14,3 +14,4 @@ regions[page_top] = Page top
 regions[page_bottom] = Page bottom
 regions[sidebar_first] = First sidebar
 regions_hidden[] = sidebar_first
+type = admin-theme