diff --git a/core/modules/system/src/Tests/System/ThemeTest.php b/core/modules/system/src/Tests/System/ThemeTest.php
index 557a05c..2e15bfe 100644
--- a/core/modules/system/src/Tests/System/ThemeTest.php
+++ b/core/modules/system/src/Tests/System/ThemeTest.php
@@ -249,8 +249,14 @@ function testAdministrationTheme() {
    * Test switching the default theme.
    */
   function testSwitchDefaultTheme() {
+    /** @var \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler */
+    $theme_handler = \Drupal::service('theme_handler');
+    // First, Install Stark and set it as the default theme programmatically.
+    $theme_handler->install(array('stark'));
+    $theme_handler->setDefault('stark');
+
     // Install Bartik and set it as the default theme.
-    \Drupal::service('theme_handler')->install(array('bartik'));
+    $theme_handler->install(array('bartik'));
     $this->drupalGet('admin/appearance');
     $this->clickLink(t('Set as default'));
     $this->assertEqual($this->config('system.theme')->get('default'), 'bartik');
@@ -260,10 +266,10 @@ function testSwitchDefaultTheme() {
     $this->assertText('Bartik(' . t('active tab') . ')', 'Default local task on blocks admin page is the default theme.');
     // Switch back to Stark and test again to test that the menu cache is cleared.
     $this->drupalGet('admin/appearance');
-    // Classy is the first 'Set as default' link.
-    $this->clickLink(t('Set as default'), 0);
+    // Stark is the second 'Set as default' link.
+    $this->clickLink(t('Set as default'), 1);
     $this->drupalGet('admin/structure/block');
-    $this->assertText('Classy(' . t('active tab') . ')', 'Default local task on blocks admin page has changed.');
+    $this->assertText('Stark(' . t('active tab') . ')', 'Default local task on blocks admin page has changed.');
   }
 
   /**
@@ -322,8 +328,8 @@ function testUninstallingThemes() {
     // base theme of bartik.
     $this->assertNoRaw('Uninstall Classy theme', 'A link to uninstall the Classy theme does not appear on the theme settings page.');
 
-    // Change the default theme to stark, stark is third in the list.
-    $this->clickLink(t('Set as default'), 2);
+    // Change the default theme to stark, stark is second in the list.
+    $this->clickLink(t('Set as default'), 1);
 
     // Check that bartik can be uninstalled now.
     $this->assertRaw('Uninstall Bartik theme', 'A link to uninstall the Bartik theme does appear on the theme settings page.');
diff --git a/core/themes/classy/classy.info.yml b/core/themes/classy/classy.info.yml
index fb5cb3e..bd47945 100644
--- a/core/themes/classy/classy.info.yml
+++ b/core/themes/classy/classy.info.yml
@@ -5,6 +5,7 @@ package: Core
 version: VERSION
 core: 8.x
 base theme: false
+hidden: true
 
 libraries:
   - classy/base
diff --git a/core/themes/stable/stable.info.yml b/core/themes/stable/stable.info.yml
index 687c434..960a683 100644
--- a/core/themes/stable/stable.info.yml
+++ b/core/themes/stable/stable.info.yml
@@ -5,3 +5,4 @@ package: Core
 version: VERSION
 core: 8.x
 base theme: false
+hidden: true