diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 2c17020..f807979 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -48,25 +48,15 @@
  */
 function drupal_theme_access($theme) {
   if (is_object($theme)) {
-    return _drupal_theme_access($theme);
+    return !empty($theme->status);
   }
   else {
     $themes = list_themes();
-    return isset($themes[$theme]) && _drupal_theme_access($themes[$theme]);
+    return !empty($themes[$theme]->status);
   }
 }
 
 /**
- * Helper function for determining access to a theme.
- *
- * @see drupal_theme_access()
- */
-function _drupal_theme_access($theme) {
-  $admin_theme = variable_get('admin_theme');
-  return !empty($theme->status) || ($admin_theme && $theme->name == $admin_theme);
-}
-
-/**
  * Initialize the theme system by loading the theme.
  */
 function drupal_theme_initialize() {
diff --git a/core/modules/block/block.module b/core/modules/block/block.module
index c07b73d..4a3d6b9 100644
--- a/core/modules/block/block.module
+++ b/core/modules/block/block.module
@@ -177,7 +177,7 @@ function block_menu() {
 }
 
 /**
- * Access callback: Only admin or enabled themes can be accessed.
+ * Access callback: Only enabled themes can be accessed.
  *
  * Path:
  * - admin/structure/block/list/% (for each theme)
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockAdminThemeTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockAdminThemeTest.php
index 7ba81c1..c3a220f 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockAdminThemeTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockAdminThemeTest.php
@@ -10,7 +10,7 @@
 use Drupal\simpletest\WebTestBase;
 
 /**
- * Test the block system with admin themes.
+ * Tests the block system with admin themes.
  */
 class BlockAdminThemeTest extends WebTestBase {
 
@@ -23,8 +23,8 @@ class BlockAdminThemeTest extends WebTestBase {
 
   public static function getInfo() {
     return array(
-      'name' => 'Admin theme block admin accessibility',
-      'description' => "Check whether the block administer page for a disabled theme accessible if and only if it's the admin theme.",
+      'name' => 'Administration theme',
+      'description' => 'Tests the block system with admin themes.',
       'group' => 'Block',
     );
   }
@@ -39,12 +39,13 @@ function testAdminTheme() {
 
     // Ensure that access to block admin page is denied when theme is disabled.
     $this->drupalGet('admin/structure/block/list/bartik');
-    $this->assertResponse(403, t('The block admin page for a disabled theme can not be accessed'));
+    $this->assertResponse(403);
 
     // Enable admin theme and confirm that tab is accessible.
+    theme_enable(array('bartik'));
     $edit['admin_theme'] = 'bartik';
     $this->drupalPost('admin/appearance', $edit, t('Save configuration'));
     $this->drupalGet('admin/structure/block/list/bartik');
-    $this->assertResponse(200, t('The block admin page for the admin theme can be accessed'));
+    $this->assertResponse(200);
   }
 }
diff --git a/core/modules/system/lib/Drupal/system/Tests/Batch/PageTest.php b/core/modules/system/lib/Drupal/system/Tests/Batch/PageTest.php
index b901239..9db8518 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Batch/PageTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Batch/PageTest.php
@@ -36,6 +36,7 @@ function testBatchProgressPageTheme() {
     // Make sure that the page which starts the batch (an administrative page)
     // is using a different theme than would normally be used by the batch API.
     variable_set('theme_default', 'bartik');
+    theme_enable(array('seven'));
     variable_set('admin_theme', 'seven');
     // Log in as an administrator who can see the administrative theme.
     $admin_user = $this->drupalCreateUser(array('view the administration theme'));
diff --git a/core/modules/system/lib/Drupal/system/Tests/Menu/RouterTest.php b/core/modules/system/lib/Drupal/system/Tests/Menu/RouterTest.php
index 780298c..5fbd472 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Menu/RouterTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Menu/RouterTest.php
@@ -93,6 +93,7 @@ function testDescriptionMenuItems() {
    * Test the theme callback when it is set to use an administrative theme.
    */
   function testThemeCallbackAdministrative() {
+    theme_enable(array('seven'));
     $this->drupalGet('menu-test/theme-callback/use-admin-theme');
     $this->assertText('Custom theme: seven. Actual theme: seven.', t('The administrative theme can be correctly set in a theme callback.'));
     $this->assertRaw('seven/style.css', t("The administrative theme's CSS appears on the page."));
@@ -102,6 +103,7 @@ function testThemeCallbackAdministrative() {
    * Test that the theme callback is properly inherited.
    */
   function testThemeCallbackInheritance() {
+    theme_enable(array('seven'));
     $this->drupalGet('menu-test/theme-callback/use-admin-theme/inheritance');
     $this->assertText('Custom theme: seven. Actual theme: seven. Theme callback inheritance is being tested.', t('Theme callback inheritance correctly uses the administrative theme.'));
     $this->assertRaw('seven/style.css', t("The administrative theme's CSS appears on the page."));
@@ -132,6 +134,7 @@ function testExoticPath() {
    */
   function testThemeCallbackMaintenanceMode() {
     config('system.maintenance')->set('enabled', 1)->save();
+    theme_enable(array('seven'));
 
     // For a regular user, the fact that the site is in maintenance mode means
     // we expect the theme callback system to be bypassed entirely.
@@ -223,7 +226,7 @@ function testHookCustomTheme() {
     // Trigger hook_custom_theme() to dynamically request the Stark theme for
     // the requested page.
     variable_set('menu_test_hook_custom_theme_name', 'stark');
-    theme_enable(array('stark'));
+    theme_enable(array('stark', 'seven'));
 
     // Visit a page that does not implement a theme callback. The above request
     // should be honored.
@@ -239,7 +242,7 @@ function testThemeCallbackHookCustomTheme() {
     // Trigger hook_custom_theme() to dynamically request the Stark theme for
     // the requested page.
     variable_set('menu_test_hook_custom_theme_name', 'stark');
-    theme_enable(array('stark'));
+    theme_enable(array('stark', 'seven'));
 
     // The menu "theme callback" should take precedence over a value set in
     // hook_custom_theme().
diff --git a/core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php b/core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php
index f1e0f22..b4139e2 100644
--- a/core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/System/ThemeTest.php
@@ -172,8 +172,8 @@ function testThemeSettings() {
    * Test the administration theme functionality.
    */
   function testAdministrationTheme() {
-    theme_enable(array('stark'));
-    variable_set('theme_default', 'stark');
+    theme_enable(array('seven'));
+
     // Enable an administration theme and show it on the node admin pages.
     $edit = array(
       'admin_theme' => 'seven',
diff --git a/core/modules/system/system.admin.inc b/core/modules/system/system.admin.inc
index 2e424ad..ac554b7 100644
--- a/core/modules/system/system.admin.inc
+++ b/core/modules/system/system.admin.inc
@@ -119,12 +119,12 @@ function system_themes_page() {
 
   $theme_default = variable_get('theme_default', 'stark');
   $theme_groups  = array();
+  $admin_theme = variable_get('admin_theme', 0);
 
   foreach ($themes as &$theme) {
     if (!empty($theme->info['hidden'])) {
       continue;
     }
-    $admin_theme_options[$theme->name] = $theme->info['name'];
     $theme->is_default = ($theme->name == $theme_default);
 
     // Identify theme screenshot.
@@ -175,12 +175,14 @@ function system_themes_page() {
       }
       if (!empty($theme->status)) {
         if (!$theme->is_default) {
-          $theme->operations[] = array(
-            'title' => t('Disable'),
-            'href' => 'admin/appearance/disable',
-            'query' => $query,
-            'attributes' => array('title' => t('Disable !theme theme', array('!theme' => $theme->info['name']))),
-          );
+          if ($theme->name != $admin_theme) {
+            $theme->operations[] = array(
+              'title' => t('Disable'),
+              'href' => 'admin/appearance/disable',
+              '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',
@@ -188,6 +190,7 @@ function system_themes_page() {
             'attributes' => array('title' => t('Set !theme as default theme', array('!theme' => $theme->info['name']))),
           );
         }
+        $admin_theme_options[$theme->name] = $theme->info['name'];
       }
       else {
         $theme->operations[] = array(
@@ -212,6 +215,10 @@ function system_themes_page() {
       $theme->classes[] = 'theme-default';
       $theme->notes[] = t('default theme');
     }
+    if ($theme->name == $admin_theme || ($theme->is_default && $admin_theme == '0')) {
+      $theme->classes[] = 'theme-admin';
+      $theme->notes[] = t('admin theme');
+    }
 
     // Sort enabled and disabled themes into their own groups.
     $theme_groups[$theme->status ? 'enabled' : 'disabled'][] = $theme;
@@ -300,8 +307,8 @@ function system_theme_disable() {
 
     // Check if the specified theme is one recognized by the system.
     if (!empty($themes[$theme])) {
-      if ($theme == variable_get('theme_default', 'stark')) {
-        // Don't disable the default theme.
+      // Do not disable the default or admin theme.
+      if ($theme == variable_get('theme_default', 'stark') || $theme == variable_get('admin_theme', 0)) {
         drupal_set_message(t('%theme is the default theme and cannot be disabled.', array('%theme' => $themes[$theme]->info['name'])), 'error');
       }
       else {
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 983c317..4cf5780 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -1881,7 +1881,7 @@ function blocked_ip_load($iid) {
 }
 
 /**
- * Menu item access callback - only admin or enabled themes can be accessed.
+ * Menu item access callback - only enabled themes can be accessed.
  */
 function _system_themes_access($theme) {
   return user_access('administer themes') && drupal_theme_access($theme);
diff --git a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/ThemeTest.php b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/ThemeTest.php
index baa5c61..b226970 100644
--- a/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/ThemeTest.php
+++ b/core/modules/taxonomy/lib/Drupal/taxonomy/Tests/ThemeTest.php
@@ -26,6 +26,7 @@ function setUp() {
     // Make sure we are using distinct default and administrative themes for
     // the duration of these tests.
     variable_set('theme_default', 'bartik');
+    theme_enable(array('seven'));
     variable_set('admin_theme', 'seven');
 
     // Create and log in as a user who has permission to add and edit taxonomy