diff --git a/core/lib/Drupal/Core/Routing/CachedUrlGenerator.php b/core/lib/Drupal/Core/Routing/CachedUrlGenerator.php
index 38ae831..1cdd9ca 100644
--- a/core/lib/Drupal/Core/Routing/CachedUrlGenerator.php
+++ b/core/lib/Drupal/Core/Routing/CachedUrlGenerator.php
@@ -17,7 +17,7 @@
 /**
  * Class used to wrap a UrlGenerator to provide caching of the generated values.
  */
-class CachedUrlGenerator implements DestructableInterface, UrlGeneratorInterface {
+class CachedUrlGenerator implements DestructableInterface, CachedUrlGeneratorInterface {
 
   /**
    * The wrapped URL generator
diff --git a/core/lib/Drupal/Core/Routing/UrlGenerator.php b/core/lib/Drupal/Core/Routing/UrlGenerator.php
index c45ab6e..ac5d5c8 100644
--- a/core/lib/Drupal/Core/Routing/UrlGenerator.php
+++ b/core/lib/Drupal/Core/Routing/UrlGenerator.php
@@ -370,10 +370,4 @@ protected function getRoute($name) {
     return $route;
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function clearCache() {
-    // Nothing to do in this class.
-  }
 }
diff --git a/core/lib/Drupal/Core/Routing/UrlGeneratorInterface.php b/core/lib/Drupal/Core/Routing/UrlGeneratorInterface.php
index e526474..62fe1ef 100644
--- a/core/lib/Drupal/Core/Routing/UrlGeneratorInterface.php
+++ b/core/lib/Drupal/Core/Routing/UrlGeneratorInterface.php
@@ -199,8 +199,4 @@ public function setBasePath($path);
    */
   public function setScriptPath($path);
 
-  /**
-   * Clears the caches of the URL generator.
-   */
-  public function clearCache();
 }
diff --git a/core/modules/language/lib/Drupal/language/Tests/LanguageListTest.php b/core/modules/language/lib/Drupal/language/Tests/LanguageListTest.php
index 46c39bf..503062c 100644
--- a/core/modules/language/lib/Drupal/language/Tests/LanguageListTest.php
+++ b/core/modules/language/lib/Drupal/language/Tests/LanguageListTest.php
@@ -46,8 +46,7 @@ function testLanguageList() {
     );
     $this->drupalPost('admin/config/regional/language/add', $edit, t('Add language'));
     $this->assertText('French', 'Language added successfully.');
-    // Check for correct page redirection.
-    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)));
+    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)), 'Correct page redirection.');
 
     // Add custom language.
     $langcode = 'xx';
@@ -59,8 +58,7 @@ function testLanguageList() {
       'direction' => '0',
     );
     $this->drupalPost('admin/config/regional/language/add', $edit, t('Add custom language'));
-    // Check for correct page redirection.
-    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)));
+    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)), 'Correct page redirection.');
     $this->assertRaw('"edit-languages-' . $langcode .'-weight"', 'Language code found.');
     $this->assertText(t($name), 'Test language added.');
 
@@ -76,13 +74,11 @@ function testLanguageList() {
     // Clear cached urls in the local process too.
     $this->container->get('url_generator')->clearCache();
     $this->assertNoOptionSelected('edit-site-default-language', 'en', 'Default language updated.');
-    // Check for correct page redirection.
-    $this->assertEqual($this->getUrl(), url($path, array('absolute' => TRUE)));
+    $this->assertEqual($this->getUrl(), url($path, array('absolute' => TRUE)), 'Correct page redirection.');
 
     // Ensure we can't delete the default language.
     $this->drupalGet('admin/config/regional/language/delete/' . $langcode);
-    // Check for correct page redirection.
-    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)));
+    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)), 'Correct page redirection.');
     $this->assertText(t('The default language cannot be deleted.'), 'Failed to delete the default language.');
 
     // Ensure 'Edit' link works.
@@ -95,8 +91,7 @@ function testLanguageList() {
     );
     $this->drupalPost('admin/config/regional/language/edit/' . $langcode, $edit, t('Save language'));
     $this->assertRaw($name, 'The language has been updated.');
-    // Check for correct page redirection.
-    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)));
+    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)), 'Correct page redirection.');
 
     // Change back the default language.
     $edit = array(
@@ -113,8 +108,7 @@ function testLanguageList() {
     $this->drupalGet('admin/config/regional/language/delete/' . $langcode);
     // First test the 'cancel' link.
     $this->clickLink(t('Cancel'));
-    // Check for correct page redirection.
-    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)));
+    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)), 'Correct page redirection.');
     $this->assertRaw($name, 'The language was not deleted.');
     // Delete the language for real. This a confirm form, we do not need any
     // fields changed.
@@ -122,8 +116,7 @@ function testLanguageList() {
     // We need raw here because %language and %langcode will add HTML.
     $t_args = array('%language' => $name, '%langcode' => $langcode);
     $this->assertRaw(t('The %language (%langcode) language has been removed.', $t_args), 'The test language has been removed.');
-    // Check for correct page redirection.
-    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)));
+    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)), 'Correct page redirection.');
     // Verify that language is no longer found.
     $this->drupalGet('admin/config/regional/language/delete/' . $langcode);
     $this->assertResponse(404, 'Language no longer found.');
@@ -142,8 +135,7 @@ function testLanguageList() {
     // We need raw here because %language and %langcode will add HTML.
     $t_args = array('%language' => 'French', '%langcode' => 'fr');
     $this->assertRaw(t('The %language (%langcode) language has been removed.', $t_args), 'Disabled language has been removed.');
-    // Check for correct page redirection.
-    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)));
+    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)), 'Correct page redirection.');
     // Verify that language is no longer found.
     $this->drupalGet('admin/config/regional/language/delete/fr');
     $this->assertResponse(404, 'Language no longer found.');
@@ -165,8 +157,7 @@ function testLanguageList() {
     $this->drupalPost('admin/config/regional/language/add', $edit, t('Add custom language'));
     // Clear cached urls in the local process too.
     $this->container->get('url_generator')->clearCache();
-    // Check for correct page redirection.
-    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)));
+    $this->assertEqual($this->getUrl(), url('admin/config/regional/language', array('absolute' => TRUE)), 'Correct page redirection.');
     $this->assertText($name, 'Name found.');
 
     // Check if we can change the default language.
@@ -181,8 +172,7 @@ function testLanguageList() {
     // Clear cached urls in the local process too.
     $this->container->get('url_generator')->clearCache();
     $this->assertNoOptionSelected('edit-site-default-language', 'en', 'Default language updated.');
-    // Check for correct page redirection.
-    $this->assertEqual($this->getUrl(), url($path, array('absolute' => TRUE)));
+    $this->assertEqual($this->getUrl(), url($path, array('absolute' => TRUE)), 'Correct page redirection.');
 
     $this->drupalPost('admin/config/regional/language/delete/en', array(), t('Delete'));
     // We need raw here because %language and %langcode will add HTML.
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
index 06dcef9..8c6cdf4 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/WebTestBase.php
@@ -15,6 +15,7 @@
 use Drupal\Core\Database\ConnectionNotDefinedException;
 use Drupal\Core\Language\Language;
 use Drupal\Core\Routing\CachedUrlGenerator;
+use Drupal\Core\Routing\CachedUrlGeneratorInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Session\UserSession;
 use Drupal\Core\StreamWrapper\PublicStream;
@@ -3404,7 +3405,9 @@ protected function prepareRequestForGenerator($clean_urls = TRUE, $override_serv
     $generator->setRequest($request);
 
     // Ensure any internal caches of the URL generator are cleared.
-    $generator->clearCache();
+    if ($generator instanceof CachedUrlGeneratorInterface) {
+      $generator->clearCache();
+    }
 
     return $request;
   }
diff --git a/core/modules/system/lib/Drupal/system/Form/RegionalForm.php b/core/modules/system/lib/Drupal/system/Form/RegionalForm.php
index f47a104..7a1e735 100644
--- a/core/modules/system/lib/Drupal/system/Form/RegionalForm.php
+++ b/core/modules/system/lib/Drupal/system/Form/RegionalForm.php
@@ -10,6 +10,7 @@
 use Drupal\Core\Config\ConfigFactory;
 use Drupal\Core\Config\Context\ContextInterface;
 use Drupal\Core\Locale\CountryManagerInterface;
+use Drupal\Core\Routing\CachedUrlGeneratorInterface;
 use Drupal\Core\Routing\UrlGeneratorInterface;
 use Drupal\system\SystemConfigFormBase;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -166,7 +167,9 @@ public function submitForm(array &$form, array &$form_state) {
       ->set('timezone.user.default', $form_state['values']['user_default_timezone'])
       ->save();
 
-    $this->urlGenerator->clearCache();
+    if ($this->urlGenerator instanceof CachedUrlGeneratorInterface) {
+      $this->urlGenerator->clearCache();
+    }
 
     parent::submitForm($form, $form_state);
   }