diff --git a/core/lib/Drupal/Core/Render/Element/RenderElement.php b/core/lib/Drupal/Core/Render/Element/RenderElement.php
index f7ad74b..ca4806a 100644
--- a/core/lib/Drupal/Core/Render/Element/RenderElement.php
+++ b/core/lib/Drupal/Core/Render/Element/RenderElement.php
@@ -240,7 +240,12 @@ public static function preRenderAjaxForm($element) {
         // to hide the password field dynamically.
         $query = \Drupal::request()->query->all();
         $query[FormBuilderInterface::AJAX_FORM_REQUEST] = TRUE;
-        $settings['url'] = Url::fromRoute('<current>', [], ['query' => $query])->toString();
+
+        $settings += ['options' => []];
+        $settings['options'] += ['query' => []];
+        $options['query'] = $settings['options']['query'] + $query;
+
+        $settings['url'] = Url::fromRoute('<current>', [], $options)->toString();
       }
 
       // @todo Legacy support. Remove in Drupal 8.
diff --git a/core/modules/system/src/Tests/Ajax/AjaxFormCacheTest.php b/core/modules/system/src/Tests/Ajax/AjaxFormCacheTest.php
index f151c33..cc91f03 100644
--- a/core/modules/system/src/Tests/Ajax/AjaxFormCacheTest.php
+++ b/core/modules/system/src/Tests/Ajax/AjaxFormCacheTest.php
@@ -44,8 +44,9 @@ public function testFormCacheUsage() {
     $this->drupalGet($cached_form_url);
     $this->drupalGet($cached_form_url);
 
-    // The number of cache entries should be exactly 3.
-    $this->assertEqual(3, count($key_value_expirable->getAll()));
+    // The number of cache entries should be exactly 0, we just start to cache
+    // once we have a POST request.
+    $this->assertEqual(0, count($key_value_expirable->getAll()));
   }
 
   /**
diff --git a/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestCachedForm.php b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestCachedForm.php
index 3b22783..61122bf 100644
--- a/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestCachedForm.php
+++ b/core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestCachedForm.php
@@ -34,9 +34,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
         'option1' => $this->t('Option 1'),
         'option2' => $this->t('Option 2'),
       ],
-      '#ajax' => [
-        'url' => Url::fromRoute('system.ajax'),
-      ],
+      '#ajax' => [],
     ];
     return $form;
   }
diff --git a/core/tests/Drupal/Tests/Core/Render/Element/RenderElementTest.php b/core/tests/Drupal/Tests/Core/Render/Element/RenderElementTest.php
index 2f1bf66..bdbf5ef 100644
--- a/core/tests/Drupal/Tests/Core/Render/Element/RenderElementTest.php
+++ b/core/tests/Drupal/Tests/Core/Render/Element/RenderElementTest.php
@@ -21,17 +21,38 @@
 class RenderElementTest extends UnitTestCase {
 
   /**
+   * The request stack.
+   *
+   * @var \Symfony\Component\HttpFoundation\RequestStack
+   */
+  protected $requestStack;
+
+  /**
+   * The container.
+   *
+   * @var \Drupal\Core\DependencyInjection\ContainerBuilder
+   */
+  protected $container;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->requestStack = new RequestStack();
+    $this->container = new ContainerBuilder();
+    $this->container->set('request_stack', $this->requestStack);
+    \Drupal::setContainer($this->container);
+  }
+
+  /**
    * @covers ::preRenderAjaxForm
    */
   public function testPreRenderAjaxForm() {
-    $request_stack = new RequestStack();
-    $container = new ContainerBuilder();
-    $container->set('request_stack', $request_stack);
-    \Drupal::setContainer($container);
-
     $request = Request::create('/test');
     $request->query->set('foo', 'bar');
-    $request_stack->push($request);
+    $this->requestStack->push($request);
 
     $prophecy = $this->prophesize('Drupal\Core\Routing\UrlGeneratorInterface');
     $url = '/test?foo=bar&ajax_form=1';
@@ -39,7 +60,7 @@ public function testPreRenderAjaxForm() {
       ->willReturn($url);
 
     $url_generator = $prophecy->reveal();
-    $container->set('url_generator', $url_generator);
+    $this->container->set('url_generator', $url_generator);
 
     $element = [
       '#type' => 'select',
@@ -55,4 +76,41 @@ public function testPreRenderAjaxForm() {
     $this->assertTrue($element['#ajax_processed']);
     $this->assertEquals($url, $element['#attached']['drupalSettings']['ajax']['test']['url']);
   }
+
+  /**
+   * @covers ::preRenderAjaxForm
+   */
+  public function testPreRenderAjaxFormWithQueryOptions() {
+    $request = Request::create('/test');
+    $request->query->set('foo', 'bar');
+    $this->requestStack->push($request);
+
+    $prophecy = $this->prophesize('Drupal\Core\Routing\UrlGeneratorInterface');
+    $url = '/test?foo=bar&other=query&ajax_form=1';
+    $prophecy->generateFromRoute('<current>', [], ['query' => ['foo' => 'bar', 'other' => 'query', FormBuilderInterface::AJAX_FORM_REQUEST => TRUE]], FALSE)
+      ->willReturn($url);
+
+    $url_generator = $prophecy->reveal();
+    $this->container->set('url_generator', $url_generator);
+
+    $element = [
+      '#type' => 'select',
+      '#id' => 'test',
+      '#ajax' => [
+        'wrapper' => 'foo',
+        'callback' => 'test-callback',
+        'options' => [
+          'query' => [
+            'other' => 'query',
+          ]
+        ]
+      ],
+    ];
+
+    $element = RenderElement::preRenderAjaxForm($element);
+
+    $this->assertTrue($element['#ajax_processed']);
+    $this->assertEquals($url, $element['#attached']['drupalSettings']['ajax']['test']['url']);
+  }
+
 }