diff --git a/core/lib/Drupal/Core/Form/FormBuilder.php b/core/lib/Drupal/Core/Form/FormBuilder.php
index d33daa1..a77632f 100644
--- a/core/lib/Drupal/Core/Form/FormBuilder.php
+++ b/core/lib/Drupal/Core/Form/FormBuilder.php
@@ -19,7 +19,6 @@
 use Drupal\Core\Render\Element;
 use Drupal\Core\Render\ElementInfoManagerInterface;
 use Drupal\Core\Theme\ThemeManagerInterface;
-use Drupal\Core\Url;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 use Symfony\Component\HttpFoundation\RequestStack;
 use Symfony\Component\HttpFoundation\Response;
@@ -685,25 +684,15 @@ public function prepareForm($form_id, &$form, FormStateInterface &$form_state) {
    *   The URL to be used as the $form['#action'].
    */
   protected function buildFormAction() {
-    $request = $this->requestStack->getMasterRequest();
-
-    // Do not attempt to use \Drupal\Core\Url during installation,
-    // return the request URI directly.
-    if (drupal_installation_attempted()) {
-      return $request->getRequestUri();
-    }
-
     // @todo Use <current> instead of the master request in
     //   https://www.drupal.org/node/2505339.
-    $url = Url::fromUri('internal:' . $request->getRequestUri());
+    $request_uri = $this->requestStack->getMasterRequest()->getRequestUri();
 
     // @todo Remove this unset() once these are removed from the request in
     //   https://www.drupal.org/node/2504709.
-    $query = $url->getOption('query');
-    unset($query[FormBuilderInterface::AJAX_FORM_REQUEST], $query[MainContentViewSubscriber::WRAPPER_FORMAT]);
-    $url->setOption('query', $query);
-
-    return $url->toString();
+    $parsed = UrlHelper::parse($request_uri);
+    unset($parsed['query'][FormBuilderInterface::AJAX_FORM_REQUEST], $parsed['query'][MainContentViewSubscriber::WRAPPER_FORMAT]);
+    return $parsed['path'] . ($parsed['query'] ? ('?' . UrlHelper::buildQuery($parsed['query'])) : '');
   }
 
   /**
diff --git a/core/modules/dblog/src/Tests/DbLogFormInjectionTest.php b/core/modules/dblog/src/Tests/DbLogFormInjectionTest.php
index af69263..e622fe2 100644
--- a/core/modules/dblog/src/Tests/DbLogFormInjectionTest.php
+++ b/core/modules/dblog/src/Tests/DbLogFormInjectionTest.php
@@ -83,10 +83,8 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
   protected function setUp() {
     parent::setUp();
     $this->installSchema('dblog', ['watchdog']);
-    $this->installSchema('system', ['key_value_expire', 'router', 'sequences']);
+    $this->installSchema('system', ['key_value_expire', 'sequences']);
     $this->installEntitySchema('user');
-    \Drupal::service('router.builder')->rebuild();
-
     $this->logger = \Drupal::logger('test_logger');
     $test_user = User::create(array(
       'name' => 'foobar',
diff --git a/core/modules/language/src/Tests/LanguageListTest.php b/core/modules/language/src/Tests/LanguageListTest.php
index 252b6d3..e72a6b0 100644
--- a/core/modules/language/src/Tests/LanguageListTest.php
+++ b/core/modules/language/src/Tests/LanguageListTest.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\language\Tests;
 
-use Drupal\Core\Url;
 use Drupal\language\Entity\ConfigurableLanguage;
 use Drupal\simpletest\WebTestBase;
 use Drupal\Core\Language\Language;
@@ -137,11 +136,7 @@ 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), 'The French language has been removed.');
-    // The previous request had still two languages (before the container
-    // rebuild), so the form pointed to /en. Now that we removed 'fr',
-    // \Drupal::url() will no longer take language url processing in mind,
-    // therefore add a manual prefix.
-    $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE, 'prefix' => $english->getId() . '/']));
+    $this->assertUrl(\Drupal::url('entity.configurable_language.collection', [], ['absolute' => TRUE]));
     // Verify that language is no longer found.
     $this->drupalGet('admin/config/regional/language/delete/fr');
     $this->assertResponse(404, 'Language no longer found.');
diff --git a/core/modules/system/src/Tests/Form/FormDefaultHandlersTest.php b/core/modules/system/src/Tests/Form/FormDefaultHandlersTest.php
index de3b596..94187af 100644
--- a/core/modules/system/src/Tests/Form/FormDefaultHandlersTest.php
+++ b/core/modules/system/src/Tests/Form/FormDefaultHandlersTest.php
@@ -31,8 +31,7 @@ class FormDefaultHandlersTest extends KernelTestBase implements FormInterface {
    */
   protected function setUp() {
     parent::setUp();
-    $this->installSchema('system', ['key_value_expire', 'router']);
-    \Drupal::service('router.builder')->rebuild();
+    $this->installSchema('system', ['key_value_expire']);
   }
 
   /**
diff --git a/core/modules/system/src/Tests/Form/RedirectTest.php b/core/modules/system/src/Tests/Form/RedirectTest.php
index aface9e..6ea944c 100644
--- a/core/modules/system/src/Tests/Form/RedirectTest.php
+++ b/core/modules/system/src/Tests/Form/RedirectTest.php
@@ -97,7 +97,7 @@ public function testRedirectFromErrorPages() {
     $this->assertResponse(404);
     $this->drupalPostForm(NULL, array(), t('Submit'));
     $this->assertResponse(200);
-    $this->assertUrl($expected);
+    $this->assertUrl($expected, [], 'Redirected to correct url/query.');
 
     // Visit the block admin page (403 page) and submit the form. Verify it
     // ends up at the right URL.
@@ -105,6 +105,6 @@ public function testRedirectFromErrorPages() {
     $this->assertResponse(403);
     $this->drupalPostForm(NULL, array(), t('Submit'));
     $this->assertResponse(200);
-    $this->assertUrl($expected);
+    $this->assertUrl($expected, [], 'Redirected to correct url/query.');
   }
 }
diff --git a/core/modules/system/src/Tests/Queue/QueueSerializationTest.php b/core/modules/system/src/Tests/Queue/QueueSerializationTest.php
index 584d8ba..9108ac2 100644
--- a/core/modules/system/src/Tests/Queue/QueueSerializationTest.php
+++ b/core/modules/system/src/Tests/Queue/QueueSerializationTest.php
@@ -81,10 +81,8 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
    */
   protected function setUp() {
     parent::setUp();
-    $this->installSchema('system', ['key_value_expire', 'router', 'sequences', 'queue']);
+    $this->installSchema('system', ['key_value_expire', 'sequences', 'queue']);
     $this->installEntitySchema('user');
-    \Drupal::service('router.builder')->rebuild();
-
     $this->queue = \Drupal::service('queue.database')->get('aggregator_refresh');
     $test_user = User::create(array(
       'name' => 'foobar',
diff --git a/core/modules/user/src/Tests/UserAccountFormFieldsTest.php b/core/modules/user/src/Tests/UserAccountFormFieldsTest.php
index 0e22d19..679eec0 100644
--- a/core/modules/user/src/Tests/UserAccountFormFieldsTest.php
+++ b/core/modules/user/src/Tests/UserAccountFormFieldsTest.php
@@ -26,16 +26,6 @@ class UserAccountFormFieldsTest extends KernelTestBase {
   public static $modules = array('system', 'user', 'field');
 
   /**
-   * {@inheritdoc}
-   */
-  protected function setUp() {
-    parent::setUp();
-
-    $this->installSchema('system', ['router']);
-    \Drupal::service('router.builder')->rebuild();
-  }
-
-  /**
    * Tests the root user account form section in the "Configure site" form.
    */
   function testInstallConfigureForm() {
@@ -88,6 +78,10 @@ function testUserEditForm() {
     // Install default configuration; required for AccountFormController.
     $this->installConfig(array('user'));
 
+    // Install the router table and then rebuild.
+    $this->installSchema('system', ['router']);
+    \Drupal::service('router.builder')->rebuild();
+
     $form = $this->buildAccountForm('default');
 
     // Verify name and pass field order.
diff --git a/core/tests/Drupal/Tests/Core/Form/FormTestBase.php b/core/tests/Drupal/Tests/Core/Form/FormTestBase.php
index 5b8d1ab..b6fe9dd 100644
--- a/core/tests/Drupal/Tests/Core/Form/FormTestBase.php
+++ b/core/tests/Drupal/Tests/Core/Form/FormTestBase.php
@@ -189,10 +189,7 @@ protected function setUp() {
       ->getMock();
     $this->root = dirname(dirname(substr(__DIR__, 0, -strlen(__NAMESPACE__))));
 
-    $this->formBuilder = $this->getMockBuilder('Drupal\Core\Form\FormBuilder')
-      ->setConstructorArgs([$this->formValidator, $this->formSubmitter, $this->formCache, $this->moduleHandler, $this->eventDispatcher, $this->requestStack, $this->classResolver, $this->elementInfo, $this->themeManager, $this->csrfToken, $this->kernel])
-      ->setMethods(['buildFormAction'])
-      ->getMock();
+    $this->formBuilder = new FormBuilder($this->formValidator, $this->formSubmitter, $this->formCache, $this->moduleHandler, $this->eventDispatcher, $this->requestStack, $this->classResolver, $this->elementInfo, $this->themeManager, $this->csrfToken, $this->kernel);
   }
 
   /**