diff --git a/core/lib/Drupal/Core/Theme/MissingThemeDependencyException.php b/core/lib/Drupal/Core/Theme/MissingThemeDependencyException.php
new file mode 100644
index 0000000..c3f72af
--- /dev/null
+++ b/core/lib/Drupal/Core/Theme/MissingThemeDependencyException.php
@@ -0,0 +1,48 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Theme\MissingThemeDependencyException.
+ */
+
+namespace Drupal\Core\Theme;
+
+/**
+ * Exception to be thrown when base theme for installed theme is not installed.
+ *
+ * @see \Drupal\Core\Theme\ThemeInitialization::getActiveThemeByName().
+ * @see \Drupal\system\Controller\DbUpdateController::ensureActiveThemeDependencies().
+ */
+class MissingThemeDependencyException extends \Exception {
+
+  /**
+   * The missing theme dependency.
+   *
+   * @var string
+   */
+  protected $theme;
+
+  /**
+   * Constructs the exception.
+   *
+   * @param string $message
+   *   The exception message.
+   * @param string $theme
+   *   The missing theme dependency.
+   */
+  public function __construct($message, $theme) {
+    parent::__construct($message);
+    $this->theme = $theme;
+  }
+
+  /**
+   * Gets the machine name of the missing theme.
+   *
+   * @return string
+   *   The machine name of the theme that is missing.
+   */
+  public function getMissingThemeName() {
+    return $this->theme;
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Theme/ThemeInitialization.php b/core/lib/Drupal/Core/Theme/ThemeInitialization.php
index 95f27a9..af4b2c6 100644
--- a/core/lib/Drupal/Core/Theme/ThemeInitialization.php
+++ b/core/lib/Drupal/Core/Theme/ThemeInitialization.php
@@ -109,6 +109,9 @@ public function getActiveThemeByName($theme_name) {
     $ancestor = $theme_name;
     while ($ancestor && isset($themes[$ancestor]->base_theme)) {
       $ancestor = $themes[$ancestor]->base_theme;
+      if (!$this->themeHandler->themeExists($ancestor)) {
+        throw new MissingThemeDependencyException(sprintf('Base theme %s has not been installed.', $ancestor), $ancestor);
+      }
       $base_themes[] = $themes[$ancestor];
     }
 
diff --git a/core/lib/Drupal/Core/Theme/ThemeInitializationInterface.php b/core/lib/Drupal/Core/Theme/ThemeInitializationInterface.php
index f2b1547..cd5c1be 100644
--- a/core/lib/Drupal/Core/Theme/ThemeInitializationInterface.php
+++ b/core/lib/Drupal/Core/Theme/ThemeInitializationInterface.php
@@ -34,6 +34,9 @@ public function initTheme($theme_name);
    *
    * @return \Drupal\Core\Theme\ActiveTheme
    *   An active theme object instance for the given theme.
+   *
+   * @throws \Drupal\Core\Theme\MissingThemeDependencyException
+   *   Thrown when base theme for installed theme is not installed.
    */
   public function getActiveThemeByName($theme_name);
 
diff --git a/core/modules/config/src/Tests/ConfigImportInstallProfileTest.php b/core/modules/config/src/Tests/ConfigImportInstallProfileTest.php
index 19ef2ee..e15d3ac 100644
--- a/core/modules/config/src/Tests/ConfigImportInstallProfileTest.php
+++ b/core/modules/config/src/Tests/ConfigImportInstallProfileTest.php
@@ -67,6 +67,7 @@ public function testInstallProfileValidation() {
     $core['module']['testing_config_import'] = 0;
     unset($core['module']['syslog']);
     unset($core['theme']['stark']);
+    $core['theme']['stable'] = 0;
     $core['theme']['classy'] = 0;
     $sync->write('core.extension', $core);
     $sync->deleteAll('syslog.');
diff --git a/core/modules/system/src/Controller/DbUpdateController.php b/core/modules/system/src/Controller/DbUpdateController.php
index 0239a41..329acf6 100644
--- a/core/modules/system/src/Controller/DbUpdateController.php
+++ b/core/modules/system/src/Controller/DbUpdateController.php
@@ -10,11 +10,15 @@
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Controller\ControllerBase;
 use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Extension\ThemeHandlerInterface;
+use Drupal\Core\Extension\ThemeInstallerInterface;
 use Drupal\Core\KeyValueStore\KeyValueExpirableFactoryInterface;
 use Drupal\Core\Render\BareHtmlPageRendererInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Site\Settings;
 use Drupal\Core\State\StateInterface;
+use Drupal\Core\Theme\MissingThemeDependencyException;
+use Drupal\Core\Theme\ThemeManagerInterface;
 use Drupal\Core\Update\UpdateRegistry;
 use Drupal\Core\Url;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -83,6 +87,27 @@ class DbUpdateController extends ControllerBase {
   protected $postUpdateRegistry;
 
   /**
+   * The theme manager.
+   *
+   * @var \Drupal\Core\Theme\ThemeManagerInterface
+   */
+  protected $themeManager;
+
+  /**
+   * The theme handler.
+   *
+   * @var \Drupal\Core\Extension\ThemeHandlerInterface
+   */
+  protected $themeHandler;
+
+  /**
+   * The theme installer.
+   *
+   * @var \Drupal\Core\Extension\ThemeInstallerInterface
+   */
+  protected $themeInstaller;
+
+  /**
    * Constructs a new UpdateController.
    *
    * @param string $root
@@ -101,8 +126,14 @@ class DbUpdateController extends ControllerBase {
    *   The bare HTML page renderer.
    * @param \Drupal\Core\Update\UpdateRegistry $post_update_registry
    *   The post update registry.
+   * @param \Drupal\Core\Theme\ThemeManagerInterface $theme_manager
+   *   The theme manager.
+   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
+   *   The theme handler.
+   * @param \Drupal\Core\Extension\ThemeInstallerInterface $theme_installer
+   *   The theme installer.
    */
-  public function __construct($root, KeyValueExpirableFactoryInterface $key_value_expirable_factory, CacheBackendInterface $cache, StateInterface $state, ModuleHandlerInterface $module_handler, AccountInterface $account, BareHtmlPageRendererInterface $bare_html_page_renderer, UpdateRegistry $post_update_registry) {
+  public function __construct($root, KeyValueExpirableFactoryInterface $key_value_expirable_factory, CacheBackendInterface $cache, StateInterface $state, ModuleHandlerInterface $module_handler, AccountInterface $account, BareHtmlPageRendererInterface $bare_html_page_renderer, UpdateRegistry $post_update_registry, ThemeManagerInterface $theme_manager, ThemeHandlerInterface $theme_handler, ThemeInstallerInterface $theme_installer) {
     $this->root = $root;
     $this->keyValueExpirableFactory = $key_value_expirable_factory;
     $this->cache = $cache;
@@ -111,6 +142,9 @@ public function __construct($root, KeyValueExpirableFactoryInterface $key_value_
     $this->account = $account;
     $this->bareHtmlPageRenderer = $bare_html_page_renderer;
     $this->postUpdateRegistry = $post_update_registry;
+    $this->themeManager = $theme_manager;
+    $this->themeHandler = $theme_handler;
+    $this->themeInstaller = $theme_installer;
   }
 
   /**
@@ -125,7 +159,10 @@ public static function create(ContainerInterface $container) {
       $container->get('module_handler'),
       $container->get('current_user'),
       $container->get('bare_html_page_renderer'),
-      $container->get('update.post_update_registry')
+      $container->get('update.post_update_registry'),
+      $container->get('theme.manager'),
+      $container->get('theme_handler'),
+      $container->get('theme_installer')
     );
   }
 
@@ -150,6 +187,8 @@ public function handle($op, Request $request) {
 
     drupal_load_updates();
     update_fix_compatibility();
+    // Make sure that update pages dependencies has been met.
+    $this->ensureActiveThemeDependencies();
 
     if ($request->query->get('continue')) {
       $_SESSION['update_ignore_warnings'] = TRUE;
@@ -706,4 +745,26 @@ protected function getModuleUpdates() {
     return $return;
   }
 
+  /**
+   * Ensures that all the dependencies for active theme has been met.
+   */
+  protected function ensureActiveThemeDependencies() {
+    \Drupal::cache('bootstrap')->delete('system_list');
+    \Drupal::state()->set('system.theme.data', array());
+    // Ensure that at least the maintenance page has a working theme where all
+    // of the parent themes have been enabled.
+    do {
+      try {
+        $this->themeManager->getActiveTheme();
+        break;
+      }
+      catch (MissingThemeDependencyException $e) {
+        // If this tries to install an unknown theme then it will throw an
+        // exception.
+        $theme_installed = $this->themeInstaller->install([$e->getMissingThemeName()]);
+        $this->themeHandler->rebuildThemeData();
+      }
+    } while ($theme_installed);
+  }
+
 }
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 69044a1..97f726f 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -1810,6 +1810,9 @@ function system_update_8011() {
  */
 function system_update_8012() {
   $theme_handler = \Drupal::service('theme_handler');
+  if ($theme_handler->themeExists('stable')) {
+    return;
+  }
   // Ensure we have fresh info.
   $theme_handler->rebuildThemeData();
   foreach ($theme_handler->listInfo() as $theme) {
diff --git a/core/themes/classy/classy.info.yml b/core/themes/classy/classy.info.yml
index 2b7705b..2ad47a9 100644
--- a/core/themes/classy/classy.info.yml
+++ b/core/themes/classy/classy.info.yml
@@ -4,7 +4,6 @@ description: 'A base theme with sensible default CSS classes added. Learn how to
 package: Core
 version: VERSION
 core: 8.x
-base theme: false
 
 libraries:
   - classy/base