diff --git a/core/core.services.yml b/core/core.services.yml
index 73c7873..41b8afd 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -1119,7 +1119,7 @@ services:
     class: Drupal\Core\Extension\InfoParser
   twig:
     class: Drupal\Core\Template\TwigEnvironment
-    arguments: ['@app.root', '@twig.loader', '@module_handler', '@theme_handler', '%twig.config%']
+    arguments: ['@app.root', '@twig.loader', '%twig.config%']
     tags:
       - { name: service_collector, tag: 'twig.extension', call: addExtension }
   twig.extension:
@@ -1136,10 +1136,24 @@ services:
     tags:
       - { name: twig.extension }
   twig.loader:
-    alias: twig.loader.filesystem
+    class: Twig_Loader_Chain
+    public: false
+    tags:
+      - { name: service_collector, tag: twig.loader, call: addLoader, required: TRUE }
   twig.loader.filesystem:
-    class: Twig_Loader_Filesystem
-    arguments: ['@app.root']
+    class: Drupal\Core\Template\Loader\FilesystemLoader
+    arguments: ['@app.root', '@module_handler', '@theme_handler']
+    tags:
+      - { name: twig.loader, priority: 100 }
+  twig.loader.theme_registry:
+    class: Drupal\Core\Template\Loader\ThemeRegistryLoader
+    arguments: ['@theme.registry']
+    tags:
+      - { name: twig.loader, priority: 0 }
+  twig.loader.string:
+    class: Twig_Loader_String
+    tags:
+      - { name: twig.loader, priority: -100 }
   element_info:
     alias: plugin.manager.element_info
   file.mime_type.guesser:
diff --git a/core/lib/Drupal/Core/DependencyInjection/Compiler/TaggedHandlersPass.php b/core/lib/Drupal/Core/DependencyInjection/Compiler/TaggedHandlersPass.php
index 18927ca..fb733ba 100644
--- a/core/lib/Drupal/Core/DependencyInjection/Compiler/TaggedHandlersPass.php
+++ b/core/lib/Drupal/Core/DependencyInjection/Compiler/TaggedHandlersPass.php
@@ -53,6 +53,8 @@ class TaggedHandlersPass implements CompilerPassInterface {
    *   - Optionally the handler's priority as second argument, if the method
    *     accepts a second parameter and its name is "priority". In any case, all
    *     handlers registered at compile time are sorted already.
+   * - required: Boolean indicating if at least one handler service is required.
+   *   Defaults to FALSE.
    *
    * Example (YAML):
    * @code
@@ -74,12 +76,15 @@ class TaggedHandlersPass implements CompilerPassInterface {
    *   interface.
    * @throws \Symfony\Component\DependencyInjection\Exception\LogicException
    *   If a tagged handler does not implement the required interface.
+   * @throws \Symfony\Component\DependencyInjection\Exception\LogicException
+   *   If at least one tagged service is required but none are found.
    */
   public function process(ContainerBuilder $container) {
     foreach ($container->findTaggedServiceIds('service_collector') as $consumer_id => $passes) {
       foreach ($passes as $pass) {
         $tag = isset($pass['tag']) ? $pass['tag'] : $consumer_id;
         $method_name = isset($pass['call']) ? $pass['call'] : 'addHandler';
+        $required = isset($pass['required']) ? $pass['required'] : FALSE;
 
         // Determine parameters.
         $consumer = $container->getDefinition($consumer_id);
@@ -122,6 +127,9 @@ public function process(ContainerBuilder $container) {
           $handlers[$id] = isset($attributes[0]['priority']) ? $attributes[0]['priority'] : 0;
         }
         if (empty($handlers)) {
+          if ($required) {
+            throw new LogicException(sprintf("At least one service tagged with '%s' is required.", $tag));
+          }
           continue;
         }
         // Sort all handlers by priority.
diff --git a/core/lib/Drupal/Core/Template/Loader/FilesystemLoader.php b/core/lib/Drupal/Core/Template/Loader/FilesystemLoader.php
new file mode 100644
index 0000000..f909809
--- /dev/null
+++ b/core/lib/Drupal/Core/Template/Loader/FilesystemLoader.php
@@ -0,0 +1,52 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Template\Loader\FilesystemLoader.
+ */
+
+namespace Drupal\Core\Template\Loader;
+
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Extension\ThemeHandlerInterface;
+
+/**
+ * Loads templates from the filesystem.
+ *
+ * This loader adds module and theme template paths as namespaces to the Twig
+ * filesystem loader so that templates can be referenced by namespace, like
+ * @block/block.html.twig or @mytheme/page.html.twig.
+ */
+class FilesystemLoader extends \Twig_Loader_Filesystem {
+
+  /**
+   * Constructs a new FilesystemLoader object.
+   *
+   * @param string|array $paths
+   *   A path or an array of paths to check for templates.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   *   The module handler service.
+   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
+   *   The theme handler service.
+   */
+  public function __construct($paths = array(), ModuleHandlerInterface $module_handler, ThemeHandlerInterface $theme_handler) {
+    parent::__construct($paths);
+
+    // Add namespaced paths for modules and themes.
+    $namespaces = array();
+    foreach ($module_handler->getModuleList() as $name => $extension) {
+      $namespaces[$name] = $extension->getPath();
+    }
+    foreach ($theme_handler->listInfo() as $name => $extension) {
+      $namespaces[$name] = $extension->getPath();
+    }
+
+    foreach ($namespaces as $name => $path) {
+      $templatesDirectory = $path . '/templates';
+      if (file_exists($templatesDirectory)) {
+        $this->addPath($templatesDirectory, $name);
+      }
+    }
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Template/Loader/ThemeRegistryLoader.php b/core/lib/Drupal/Core/Template/Loader/ThemeRegistryLoader.php
new file mode 100644
index 0000000..fe1ae25
--- /dev/null
+++ b/core/lib/Drupal/Core/Template/Loader/ThemeRegistryLoader.php
@@ -0,0 +1,69 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Template\Loader\ThemeRegistryLoader.
+ */
+
+namespace Drupal\Core\Template\Loader;
+
+use Drupal\Core\Theme\Registry;
+
+/**
+ * Loads templates based on information from the Drupal theme registry.
+ *
+ * Allows for template inheritance based on the currently active template.
+ */
+class ThemeRegistryLoader extends \Twig_Loader_Filesystem {
+
+  /**
+   * The theme registry used to determine which template to use.
+   *
+   * @var \Drupal\Core\Theme\Registry
+   */
+  protected $themeRegistry;
+
+  /**
+   * Constructs a new ThemeRegistryLoader object.
+   *
+   * @param \Drupal\Core\Theme\Registry $theme_registry
+   *   The theme registry.
+   */
+  public function __construct(Registry $theme_registry) {
+    $this->themeRegistry = $theme_registry;
+  }
+
+  /**
+   * Finds the path to the requested template.
+   *
+   * @param string $name
+   *   The name of the template to load.
+   *
+   * @return string
+   *   The path to the template.
+   *
+   * @throws \Twig_Error_Loader
+   *   Thrown if a template matching $name cannot be found.
+   */
+  protected function findTemplate($name) {
+    // Allow for loading based on the Drupal theme registry.
+    $hook = str_replace('.html.twig', '', strtr($name, '-', '_'));
+    $theme_registry = $this->themeRegistry->getRuntime();
+
+    if ($theme_registry->has($hook)) {
+      $info = $theme_registry->get($hook);
+      if (isset($info['path'])) {
+        $path = $info['path'] . '/' . $name;
+      }
+      elseif (isset($info['template'])) {
+        $path = $info['template'] . '.html.twig';
+      }
+      if (isset($path) && is_file($path)) {
+        return $this->cache[$name] = $path;
+      }
+    }
+
+    throw new \Twig_Error_Loader(sprintf('Unable to find template "%s" in the Drupal theme registry.', $name));
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Template/TwigEnvironment.php b/core/lib/Drupal/Core/Template/TwigEnvironment.php
index 3716277..e09d9f6 100644
--- a/core/lib/Drupal/Core/Template/TwigEnvironment.php
+++ b/core/lib/Drupal/Core/Template/TwigEnvironment.php
@@ -8,8 +8,6 @@
 namespace Drupal\Core\Template;
 
 use Drupal\Core\PhpStorage\PhpStorageFactory;
-use Drupal\Core\Extension\ModuleHandlerInterface;
-use Drupal\Core\Extension\ThemeHandlerInterface;
 
 /**
  * A class that defines a Twig environment for Drupal.
@@ -35,9 +33,13 @@ class TwigEnvironment extends \Twig_Environment {
    * internally.
    *
    * @param string $root
-   *   The app root;
+   *   The app root.
+   * @param \Twig_LoaderInterface $loader
+   *   The Twig loader or loader chain.
+   * @param array $options
+   *   The options for the Twig environment.
    */
-  public function __construct($root, \Twig_LoaderInterface $loader = NULL, ModuleHandlerInterface $module_handler, ThemeHandlerInterface $theme_handler, $options = array()) {
+  public function __construct($root, \Twig_LoaderInterface $loader = NULL, $options = array()) {
     // @todo Pass as arguments from the DIC.
     $this->cache_object = \Drupal::cache();
 
@@ -45,22 +47,6 @@ public function __construct($root, \Twig_LoaderInterface $loader = NULL, ModuleH
     // template because functions like twig_drupal_escape_filter are called.
     require_once $root . '/core/themes/engines/twig/twig.engine';
 
-    // Set twig path namespace for themes and modules.
-    $namespaces = array();
-    foreach ($module_handler->getModuleList() as $name => $extension) {
-      $namespaces[$name] = $extension->getPath();
-    }
-    foreach ($theme_handler->listInfo() as $name => $extension) {
-      $namespaces[$name] = $extension->getPath();
-    }
-
-    foreach ($namespaces as $name => $path) {
-      $templatesDirectory = $path . '/templates';
-      if (file_exists($templatesDirectory)) {
-        $loader->addPath($templatesDirectory, $name);
-      }
-    }
-
     $this->templateClasses = array();
 
     $options += array(
@@ -72,7 +58,7 @@ public function __construct($root, \Twig_LoaderInterface $loader = NULL, ModuleH
     // Ensure autoescaping is always on.
     $options['autoescape'] = TRUE;
 
-    $this->loader = new \Twig_Loader_Chain([$loader, new \Twig_Loader_String()]);
+    $this->loader = $loader;
     parent::__construct($this->loader, $options);
   }
 
diff --git a/core/modules/system/src/Tests/Theme/TwigLoaderTest.php b/core/modules/system/src/Tests/Theme/TwigLoaderTest.php
new file mode 100644
index 0000000..91de1e4
--- /dev/null
+++ b/core/modules/system/src/Tests/Theme/TwigLoaderTest.php
@@ -0,0 +1,39 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Theme\TwigLoaderTest.
+ */
+
+namespace Drupal\system\Tests\Theme;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Tests adding Twig loaders.
+ *
+ * @group Theme
+ */
+class TwigLoaderTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = ['twig_loader_test'];
+
+  /**
+   * Tests adding an additional twig loader to the loader chain.
+   */
+  public function testTwigLoaderAddition() {
+    $environment = \Drupal::service('twig');
+
+    $template = $environment->loadTemplate('kittens');
+    $this->assertEqual($template->render(array()), 'kittens', 'Passing "kittens" to the custom Twig loader returns "kittens".');
+
+    $template = $environment->loadTemplate('meow');
+    $this->assertEqual($template->render(array()), 'cats', 'Passing something other than "kittens" to the custom Twig loader returns "cats".');
+  }
+
+}
diff --git a/core/modules/system/src/Tests/Theme/TwigRegistryLoaderTest.php b/core/modules/system/src/Tests/Theme/TwigRegistryLoaderTest.php
new file mode 100644
index 0000000..589632b
--- /dev/null
+++ b/core/modules/system/src/Tests/Theme/TwigRegistryLoaderTest.php
@@ -0,0 +1,70 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Theme\TwigRegistryLoaderTest.
+ */
+
+namespace Drupal\system\Tests\Theme;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Tests Twig registry loader.
+ *
+ * @group Theme
+ */
+class TwigRegistryLoaderTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('twig_theme_test', 'block');
+
+  /**
+   * @var \Drupal\Core\Template\TwigEnvironment
+   */
+  protected $twig;
+
+  protected function setUp() {
+    parent::setUp();
+    \Drupal::service('theme_handler')->install(array('test_theme_twig_registry_loader'));
+    $this->twig = \Drupal::service('twig');
+  }
+
+  /**
+   * Checks to see if a value is a Twig template.
+   */
+  public function assertTwigTemplate($value, $message = '', $group = 'Other') {
+    $this->assertTrue($value instanceof \Twig_Template, $message, $group);
+  }
+
+  /**
+   * Tests template discovery using the Drupal theme registry.
+   */
+  public function testTemplateDiscovery() {
+    $this->assertTwigTemplate($this->twig->resolveTemplate('block.html.twig'), 'Found block.html.twig in block module.');
+  }
+
+  /**
+   * Tests template extension and includes using the Drupal theme registry.
+   */
+  public function testTwigNamespaces() {
+    // Test the module-provided extend and insert templates.
+    $this->drupalGet('twig-theme-test/registry-loader');
+    $this->assertText('This line is from twig_theme_test/templates/twig-registry-loader-test-extend.html.twig');
+    $this->assertText('This line is from twig_theme_test/templates/twig-registry-loader-test-include.html.twig');
+
+    // Enable a theme that overrides the extend and insert templates to ensure
+    // they are picked up by the registry loader.
+    $this->config('system.theme')
+      ->set('default', 'test_theme_twig_registry_loader')
+      ->save();
+    $this->drupalGet('twig-theme-test/registry-loader');
+    $this->assertText('This line is from test_theme_twig_registry_loader/templates/twig-registry-loader-test-extend.html.twig');
+    $this->assertText('This line is from test_theme_twig_registry_loader/templates/twig-registry-loader-test-include.html.twig');
+  }
+
+}
diff --git a/core/modules/system/templates/block--system-branding-block.html.twig b/core/modules/system/templates/block--system-branding-block.html.twig
index 4cf0f1a..f648773 100644
--- a/core/modules/system/templates/block--system-branding-block.html.twig
+++ b/core/modules/system/templates/block--system-branding-block.html.twig
@@ -1,4 +1,4 @@
-{% extends "@block/block.html.twig" %}
+{% extends "block.html.twig" %}
 {#
 /**
  * @file
diff --git a/core/modules/system/tests/modules/twig_loader_test/src/Loader/TestLoader.php b/core/modules/system/tests/modules/twig_loader_test/src/Loader/TestLoader.php
new file mode 100644
index 0000000..9f32969
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_loader_test/src/Loader/TestLoader.php
@@ -0,0 +1,50 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\twig_loader_test\Loader\TestLoader.
+ */
+
+namespace Drupal\twig_loader_test\Loader;
+
+use Drupal\Core\Template\Loader;
+
+/**
+ * A test Twig loader.
+ */
+class TestLoader implements \Twig_LoaderInterface, \Twig_ExistsLoaderInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getSource($name) {
+    if ($name == 'kittens') {
+      return $name;
+    }
+    else {
+      return 'cats';
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function exists($name) {
+    return TRUE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheKey($name) {
+    return $name;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isFresh($name, $time) {
+    return TRUE;
+  }
+
+}
diff --git a/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.info.yml b/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.info.yml
new file mode 100644
index 0000000..cf04aae
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.info.yml
@@ -0,0 +1,6 @@
+name: 'Twig Loader Test'
+type: module
+description: 'Support module for testing adding Twig loaders.'
+package: Testing
+version: VERSION
+core: 8.x
diff --git a/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.services.yml b/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.services.yml
new file mode 100644
index 0000000..1b19948
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_loader_test/twig_loader_test.services.yml
@@ -0,0 +1,5 @@
+services:
+  twig_loader_test.twig.test_loader:
+    class: Drupal\twig_loader_test\Loader\TestLoader
+    tags:
+      - { name: twig.loader }
diff --git a/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php b/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
index 96fcb67..2bf5394 100644
--- a/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
+++ b/core/modules/system/tests/modules/twig_theme_test/src/TwigThemeTestController.php
@@ -58,4 +58,11 @@ public function fileUrlRender() {
     );
   }
 
+  /**
+   * Menu callback for testing the Twig registry loader.
+   */
+  public function registryLoaderRender() {
+    return array('#theme' => 'twig_registry_loader_test');
+  }
+
 }
diff --git a/core/modules/system/tests/modules/twig_theme_test/templates/twig-registry-loader-test-extend.html.twig b/core/modules/system/tests/modules/twig_theme_test/templates/twig-registry-loader-test-extend.html.twig
new file mode 100644
index 0000000..e18e68e
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/templates/twig-registry-loader-test-extend.html.twig
@@ -0,0 +1,5 @@
+This line is from twig_theme_test/templates/twig-registry-loader-test-extend.html.twig
+
+{% block content %}
+This text is in a block.
+{% endblock %}
diff --git a/core/modules/system/tests/modules/twig_theme_test/templates/twig-registry-loader-test-include.html.twig b/core/modules/system/tests/modules/twig_theme_test/templates/twig-registry-loader-test-include.html.twig
new file mode 100644
index 0000000..438fd2b
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/templates/twig-registry-loader-test-include.html.twig
@@ -0,0 +1 @@
+This line is from twig_theme_test/templates/twig-registry-loader-test-include.html.twig
diff --git a/core/modules/system/tests/modules/twig_theme_test/templates/twig-registry-loader-test.html.twig b/core/modules/system/tests/modules/twig_theme_test/templates/twig-registry-loader-test.html.twig
new file mode 100644
index 0000000..a3723b5
--- /dev/null
+++ b/core/modules/system/tests/modules/twig_theme_test/templates/twig-registry-loader-test.html.twig
@@ -0,0 +1,5 @@
+{% extends "twig-registry-loader-test-extend.html.twig" %}
+
+{% block content %}
+  {% include "twig-registry-loader-test-include.html.twig" %}
+{% endblock %}
diff --git a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
index 4a415cd..e42b020 100644
--- a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
+++ b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.module
@@ -19,6 +19,15 @@ function twig_theme_test_theme($existing, $type, $theme, $path) {
     'variables' => array(),
     'template' => 'twig_namespace_test',
   );
+  $items['twig_registry_loader_test'] = array(
+    'variables' => array(),
+  );
+  $items['twig_registry_loader_test_include'] = array(
+    'variables' => array(),
+  );
+  $items['twig_registry_loader_test_extend'] = array(
+    'variables' => array(),
+  );
   $items['twig_raw_test'] = array(
     'variables' => array('script' => ''),
   );
diff --git a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
index d2abf91..4d30bb9 100644
--- a/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
+++ b/core/modules/system/tests/modules/twig_theme_test/twig_theme_test.routing.yml
@@ -32,3 +32,10 @@ twig_theme_test_file_url:
     _controller: '\Drupal\twig_theme_test\TwigThemeTestController::fileUrlRender'
   requirements:
     _access: 'TRUE'
+
+twig_theme_test_registry_loader:
+  path: '/twig-theme-test/registry-loader'
+  defaults:
+    _controller: '\Drupal\twig_theme_test\TwigThemeTestController::registryLoaderRender'
+  requirements:
+    _access: 'TRUE'
diff --git a/core/modules/system/tests/themes/test_theme_twig_registry_loader/templates/twig-registry-loader-test-extend.html.twig b/core/modules/system/tests/themes/test_theme_twig_registry_loader/templates/twig-registry-loader-test-extend.html.twig
new file mode 100644
index 0000000..e1a9eee
--- /dev/null
+++ b/core/modules/system/tests/themes/test_theme_twig_registry_loader/templates/twig-registry-loader-test-extend.html.twig
@@ -0,0 +1,5 @@
+This line is from test_theme_twig_registry_loader/templates/twig-registry-loader-test-extend.html.twig
+
+{% block content %}
+This text is in a block.
+{% endblock %}
diff --git a/core/modules/system/tests/themes/test_theme_twig_registry_loader/templates/twig-registry-loader-test-include.html.twig b/core/modules/system/tests/themes/test_theme_twig_registry_loader/templates/twig-registry-loader-test-include.html.twig
new file mode 100644
index 0000000..3a1f395
--- /dev/null
+++ b/core/modules/system/tests/themes/test_theme_twig_registry_loader/templates/twig-registry-loader-test-include.html.twig
@@ -0,0 +1 @@
+This line is from test_theme_twig_registry_loader/templates/twig-registry-loader-test-include.html.twig
diff --git a/core/modules/system/tests/themes/test_theme_twig_registry_loader/test_theme_twig_registry_loader.info.yml b/core/modules/system/tests/themes/test_theme_twig_registry_loader/test_theme_twig_registry_loader.info.yml
new file mode 100644
index 0000000..9ee01c5
--- /dev/null
+++ b/core/modules/system/tests/themes/test_theme_twig_registry_loader/test_theme_twig_registry_loader.info.yml
@@ -0,0 +1,5 @@
+name: 'Twig registry loader test'
+type: theme
+description: 'Support module for Twig registry loader testing.'
+version: VERSION
+core: 8.x
diff --git a/core/modules/text/templates/field--text-long.html.twig b/core/modules/text/templates/field--text-long.html.twig
index 5f201f0..07ce721 100644
--- a/core/modules/text/templates/field--text-long.html.twig
+++ b/core/modules/text/templates/field--text-long.html.twig
@@ -1 +1 @@
-{% extends "@text/field--text.html.twig" %}
+{% extends "field--text.html.twig" %}
diff --git a/core/modules/text/templates/field--text-with-summary.html.twig b/core/modules/text/templates/field--text-with-summary.html.twig
index 5f201f0..07ce721 100644
--- a/core/modules/text/templates/field--text-with-summary.html.twig
+++ b/core/modules/text/templates/field--text-with-summary.html.twig
@@ -1 +1 @@
-{% extends "@text/field--text.html.twig" %}
+{% extends "field--text.html.twig" %}
diff --git a/core/modules/text/templates/field--text.html.twig b/core/modules/text/templates/field--text.html.twig
index 6a63a0c..9cd1ab9 100644
--- a/core/modules/text/templates/field--text.html.twig
+++ b/core/modules/text/templates/field--text.html.twig
@@ -1,4 +1,4 @@
-{% extends "@system/field.html.twig" %}
+{% extends "field.html.twig" %}
 {#
 /**
  * @file
diff --git a/core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/TaggedHandlersPassTest.php b/core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/TaggedHandlersPassTest.php
index dd03a1f..db6f39f 100644
--- a/core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/TaggedHandlersPassTest.php
+++ b/core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/TaggedHandlersPassTest.php
@@ -42,6 +42,25 @@ public function testProcessNoConsumers() {
   }
 
   /**
+   * Tests a required consumer with no handlers.
+   *
+   * @expectedException \Symfony\Component\DependencyInjection\Exception\LogicException
+   * @expectedExceptionMessage At least one service tagged with 'consumer_id' is required.
+   * @covers ::process
+   */
+  public function testProcessRequiredHandlers() {
+    $container = $this->buildContainer();
+    $container
+      ->register('consumer_id', __NAMESPACE__ . '\ValidConsumer')
+      ->addTag('service_collector', array(
+        'required' => TRUE,
+      ));
+
+    $handler_pass = new TaggedHandlersPass();
+    $handler_pass->process($container);
+  }
+
+  /**
    * Tests consumer with missing interface in non-production environment.
    *
    * @expectedException \Symfony\Component\DependencyInjection\Exception\LogicException
diff --git a/core/themes/bartik/templates/block--system-branding-block.html.twig b/core/themes/bartik/templates/block--system-branding-block.html.twig
index f6147a6..4a4b733 100644
--- a/core/themes/bartik/templates/block--system-branding-block.html.twig
+++ b/core/themes/bartik/templates/block--system-branding-block.html.twig
@@ -1,4 +1,4 @@
-{% extends "@block/block.html.twig" %}
+{% extends "block.html.twig" %}
 {#
 /**
  * @file