diff --git a/core/core.services.yml b/core/core.services.yml
index 9dca742..83e6b94 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -286,7 +286,7 @@ services:
     tags:
       - { name: route_enhancer, priority: 15 }
   route_enhancer.form:
-    class: Drupal\Core\Routing\Enhancer\FormEnhancer
+    class: Drupal\Core\Routing\Enhancer\HtmlFormEnhancer
     arguments: ['@content_negotiation']
     tags:
       - { name: route_enhancer, priority: 10 }
diff --git a/core/lib/Drupal/Core/AjaxController.php b/core/lib/Drupal/Core/AjaxController.php
index 31259fb..f3eed0a 100644
--- a/core/lib/Drupal/Core/AjaxController.php
+++ b/core/lib/Drupal/Core/AjaxController.php
@@ -50,6 +50,7 @@ public function content(Request $request, $_content) {
     // Remove the accept header so the subrequest does not end up back in this
     // controller.
     $request->headers->remove('accept');
+    $request->headers->remove('x-requested-with');
 
     $response = $this->container->get('http_kernel')->forward($controller, $attributes->all(), $request->query->all());
     // For successful (HTTP status 200) responses.
diff --git a/core/lib/Drupal/Core/AjaxFormController.php b/core/lib/Drupal/Core/AjaxFormController.php
new file mode 100644
index 0000000..825c46b
--- /dev/null
+++ b/core/lib/Drupal/Core/AjaxFormController.php
@@ -0,0 +1,23 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\AjaxFormController.
+ */
+
+namespace Drupal\Core;
+
+use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpFoundation\Request;
+
+class AjaxFormController extends HtmlFormController {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function content(Request $request, $_form) {
+    $form = $this->getFormBuild($request, $_form);
+    return new Respnse($form);
+  }
+
+}
diff --git a/core/lib/Drupal/Core/HtmlFormController.php b/core/lib/Drupal/Core/HtmlFormController.php
index e19d8ea..f7890a8 100644
--- a/core/lib/Drupal/Core/HtmlFormController.php
+++ b/core/lib/Drupal/Core/HtmlFormController.php
@@ -46,23 +46,7 @@ public function setContainer(ContainerInterface $container = NULL) {
    *   A response object.
    */
   public function content(Request $request, $_form) {
-    $form_object = $this->getFormObject($request, $_form);
-
-    // Using reflection, find all of the parameters needed by the form in the
-    // request attributes, skipping $form and $form_state.
-    $attributes = $request->attributes->all();
-    $reflection = new \ReflectionMethod($form_object, 'buildForm');
-    $params = $reflection->getParameters();
-    $args = array();
-    foreach (array_splice($params, 2) as $param) {
-      if (array_key_exists($param->name, $attributes)) {
-        $args[] = $attributes[$param->name];
-      }
-    }
-    $form_state['build_info']['args'] = $args;
-
-    $form_id = _drupal_form_id($form_object, $form_state);
-    $form = drupal_build_form($form_id, $form_state);
+    $form = $this->getFormBuild($request, $_form);
     return new Response(drupal_render_page($form));
   }
 
@@ -91,4 +75,36 @@ protected function getFormObject(Request $request, $form_arg) {
     return $this->container->get($form_arg);
   }
 
+  /**
+   * Build the form array for a given form.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The request object.
+   * @param callable $_form
+   *   The name of the form class for this request.
+   *
+   * @return array|mixed
+   *   The built as render array.
+   */
+  protected function getFormBuild(Request $request, $_form) {
+    $form_object = $this->getFormObject($request, $_form);
+
+    // Using reflection, find all of the parameters needed by the form in the
+    // request attributes, skipping $form and $form_state.
+    $attributes = $request->attributes->all();
+    $reflection = new \ReflectionMethod($form_object, 'buildForm');
+    $params = $reflection->getParameters();
+    $args = array();
+    foreach (array_splice($params, 2) as $param) {
+      if (array_key_exists($param->name, $attributes)) {
+        $args[] = $attributes[$param->name];
+      }
+    }
+    $form_state['build_info']['args'] = $args;
+
+    $form_id = _drupal_form_id($form_object, $form_state);
+    $form = drupal_build_form($form_id, $form_state);
+    return $form;
+  }
+
 }
diff --git a/core/lib/Drupal/Core/HttpKernel.php b/core/lib/Drupal/Core/HttpKernel.php
index ca0c002..ce3272f 100644
--- a/core/lib/Drupal/Core/HttpKernel.php
+++ b/core/lib/Drupal/Core/HttpKernel.php
@@ -72,7 +72,12 @@ public function handle(Request $request, $type = HttpKernelInterface::MASTER_REQ
      */
     public function forward($controller, array $attributes = array(), array $query = array())
     {
-        $attributes['_controller'] = $controller;
+        if (isset($controller)) {
+          $attributes['_controller'] = $controller;
+        }
+        else {
+          unset($attributes['_controller']);
+        }
         $subRequest = $this->container->get('request')->duplicate($query, null, $attributes);
 
         return $this->handle($subRequest, HttpKernelInterface::SUB_REQUEST);
diff --git a/core/lib/Drupal/Core/Routing/Enhancer/AjaxFormEnhancer.php b/core/lib/Drupal/Core/Routing/Enhancer/AjaxFormEnhancer.php
new file mode 100644
index 0000000..e03f944
--- /dev/null
+++ b/core/lib/Drupal/Core/Routing/Enhancer/AjaxFormEnhancer.php
@@ -0,0 +1,31 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Routing\Enhancer\AjaxFormEnhancer.
+ */
+
+namespace Drupal\Core\Routing\Enhancer;
+
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Enhances a form route with the appropriate controller on ajax requests..
+ */
+class AjaxFormEnhancer extends HtmlFormEnhancer {
+
+  /**
+   * Content type this enhancer targets.
+   *
+   * @var string
+   */
+  protected $targetContentType = 'drupal_ajax';
+
+  /**
+   * Controller to route matching requests to.
+   *
+   * @var string
+   */
+  protected $controller = '\Drupal\Core\Ajax\DialogController::dialog';
+
+}
diff --git a/core/lib/Drupal/Core/Routing/Enhancer/FormEnhancer.php b/core/lib/Drupal/Core/Routing/Enhancer/FormEnhancer.php
deleted file mode 100644
index b23165d..0000000
--- a/core/lib/Drupal/Core/Routing/Enhancer/FormEnhancer.php
+++ /dev/null
@@ -1,46 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\Routing\Enhancer\FormEnhancer.
- */
-
-namespace Drupal\Core\Routing\Enhancer;
-
-use Symfony\Component\HttpFoundation\Request;
-use Symfony\Cmf\Component\Routing\Enhancer\RouteEnhancerInterface;
-use Drupal\Core\ContentNegotiation;
-
-/**
- * Enhances a form route with the appropriate controller.
- */
-class FormEnhancer implements RouteEnhancerInterface {
-
-  /**
-   * Content negotiation library.
-   *
-   * @var \Drupal\CoreContentNegotiation
-   */
-  protected $negotiation;
-
-  /**
-   * Constructs a new \Drupal\Core\Routing\Enhancer\FormEnhancer object.
-   *
-   * @param \Drupal\Core\ContentNegotiation $negotiation
-   *   The Content Negotiation service.
-   */
-  public function __construct(ContentNegotiation $negotiation) {
-    $this->negotiation = $negotiation;
-  }
-
-  /**
-   * {@inhertdoc}
-   */
-  public function enhance(array $defaults, Request $request) {
-    if (empty($defaults['_controller']) && !empty($defaults['_form']) && $this->negotiation->getContentType($request) === 'html') {
-      $defaults['_controller'] = '\Drupal\Core\HtmlFormController::content';
-    }
-    return $defaults;
-  }
-
-}
diff --git a/core/lib/Drupal/Core/Routing/Enhancer/HtmlFormEnhancer.php b/core/lib/Drupal/Core/Routing/Enhancer/HtmlFormEnhancer.php
new file mode 100644
index 0000000..3ecfe77
--- /dev/null
+++ b/core/lib/Drupal/Core/Routing/Enhancer/HtmlFormEnhancer.php
@@ -0,0 +1,60 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Routing\Enhancer\HtmlFormEnhancer.
+ */
+
+namespace Drupal\Core\Routing\Enhancer;
+
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Cmf\Component\Routing\Enhancer\RouteEnhancerInterface;
+use Drupal\Core\ContentNegotiation;
+
+/**
+ * Enhances a form route with the appropriate controller on html requests.
+ */
+class HtmlFormEnhancer implements RouteEnhancerInterface {
+
+  /**
+   * Content negotiation library.
+   *
+   * @var \Drupal\Core\ContentNegotiation
+   */
+  protected $negotiation;
+
+  /**
+   * Content type this enhancer targets.
+   *
+   * @var string
+   */
+  protected $targetContentType = 'html';
+
+  /**
+   * Controller to route matching requests to.
+   *
+   * @var string
+   */
+  protected $controller = '\Drupal\Core\HtmlFormController::content';
+
+  /**
+   * Constructs a new \Drupal\Core\Routing\Enhancer\HtmlFormEnhancer object.
+   *
+   * @param \Drupal\Core\ContentNegotiation $negotiation
+   *   The Content Negotiation service.
+   */
+  public function __construct(ContentNegotiation $negotiation) {
+    $this->negotiation = $negotiation;
+  }
+
+  /**
+   * {@inhertdoc}
+   */
+  public function enhance(array $defaults, Request $request) {
+    if (empty($defaults['_controller']) && !empty($defaults['_form']) && $this->negotiation->getContentType($request) === $this->targetContentType) {
+      $defaults['_controller'] = $this->controller;
+    }
+    return $defaults;
+  }
+
+}