diff --git a/core/includes/menu.inc b/core/includes/menu.inc
index 94d0e57..4c2a367 100644
--- a/core/includes/menu.inc
+++ b/core/includes/menu.inc
@@ -985,7 +985,10 @@ function menu_item_route_access(Route $route, $href, &$map) {
     if (isset($path_bits[$index]) && preg_match('/{(?<placeholder>.*)}/', $path_bits[$index], $matches)) {
       // If that placeholder is present on the request attributes, replace the
       // placeholder in the map with the value.
-      if ($request->attributes->has($matches['placeholder'])) {
+      if ($request->attributes->get('converted')->has($matches['placeholder'])) {
+        $map[$index] = $request->attributes->get('converted')->get($matches['placeholder']);
+      }
+      elseif ($request->attributes->has($matches['placeholder'])) {
         $map[$index] = $request->attributes->get($matches['placeholder']);
       }
     }
diff --git a/core/lib/Drupal/Core/Entity/EntityAccessCheck.php b/core/lib/Drupal/Core/Entity/EntityAccessCheck.php
index eb5766c..7b91561 100644
--- a/core/lib/Drupal/Core/Entity/EntityAccessCheck.php
+++ b/core/lib/Drupal/Core/Entity/EntityAccessCheck.php
@@ -42,8 +42,8 @@ public function access(Route $route, Request $request) {
     $requirement = $route->getRequirement('_entity_access');
     list($entity_type, $operation) = explode('.', $requirement);
     // If there is valid entity of the given entity type, check its access.
-    if ($request->attributes->has('_converted_' . $entity_type)) {
-      $entity = $request->attributes->get('_converted_' . $entity_type);
+    if ($request->attributes->get('converted')->has($entity_type)) {
+      $entity = $request->attributes->get('converted')->get($entity_type);
       if ($entity instanceof EntityInterface) {
         return $entity->access($operation);
       }
diff --git a/core/lib/Drupal/Core/Entity/HtmlEntityFormController.php b/core/lib/Drupal/Core/Entity/HtmlEntityFormController.php
index b79fd90..be28296 100644
--- a/core/lib/Drupal/Core/Entity/HtmlEntityFormController.php
+++ b/core/lib/Drupal/Core/Entity/HtmlEntityFormController.php
@@ -52,8 +52,8 @@ protected function getFormObject(Request $request, $form_arg) {
     $form_arg .= '.default';
     list ($entity_type, $operation) = explode('.', $form_arg);
 
-    if ($request->attributes->has('_converted_' . $entity_type)) {
-      $entity = $request->attributes->get('_converted_' . $entity_type);
+    if ($request->attributes->get('converted')->has($entity_type)) {
+      $entity = $request->attributes->get('converted')->get($entity_type);
     }
     else {
       $entity = $manager->getStorageController($entity_type)->create(array());
diff --git a/core/modules/edit/lib/Drupal/edit/Access/EditEntityAccessCheck.php b/core/modules/edit/lib/Drupal/edit/Access/EditEntityAccessCheck.php
index 9dfbfd1..96e1023 100644
--- a/core/modules/edit/lib/Drupal/edit/Access/EditEntityAccessCheck.php
+++ b/core/modules/edit/lib/Drupal/edit/Access/EditEntityAccessCheck.php
@@ -35,7 +35,7 @@ public function access(Route $route, Request $request) {
     //   http://drupal.org/node/1798214.
     $this->validateAndUpcastRequestAttributes($request);
 
-    return $this->accessEditEntity($request->attributes->get('entity'));
+    return $this->accessEditEntity($request->attributes->get('converted')->get('entity'));
   }
 
   /**
@@ -50,8 +50,8 @@ public function accessEditEntity(EntityInterface $entity) {
    */
   protected function validateAndUpcastRequestAttributes(Request $request) {
     // Load the entity.
-    if (!is_object($entity = $request->attributes->get('entity'))) {
-      $entity_id = $entity;
+    if (!$request->attributes->get('converted')->get('entity')) {
+      $entity_id = $request->attributes->get('entity');
       $entity_type = $request->attributes->get('entity_type');
       if (!$entity_type || !entity_get_info($entity_type)) {
         throw new NotFoundHttpException();
@@ -60,7 +60,7 @@ protected function validateAndUpcastRequestAttributes(Request $request) {
       if (!$entity) {
         throw new NotFoundHttpException();
       }
-      $request->attributes->set('entity', $entity);
+      $request->attributes->get('converted')->set('entity', $entity);
     }
   }
 
diff --git a/core/modules/edit/lib/Drupal/edit/Access/EditEntityFieldAccessCheck.php b/core/modules/edit/lib/Drupal/edit/Access/EditEntityFieldAccessCheck.php
index 01511cb..18f5b25 100644
--- a/core/modules/edit/lib/Drupal/edit/Access/EditEntityFieldAccessCheck.php
+++ b/core/modules/edit/lib/Drupal/edit/Access/EditEntityFieldAccessCheck.php
@@ -35,7 +35,7 @@ public function access(Route $route, Request $request) {
     //   http://drupal.org/node/1798214.
     $this->validateAndUpcastRequestAttributes($request);
 
-    return $this->accessEditEntityField($request->attributes->get('entity'), $request->attributes->get('field_name'));
+    return $this->accessEditEntityField($request->attributes->get('converted')->get('entity'), $request->attributes->get('field_name'));
   }
 
   /**
@@ -50,8 +50,8 @@ public function accessEditEntityField(EntityInterface $entity, $field_name) {
    */
   protected function validateAndUpcastRequestAttributes(Request $request) {
     // Load the entity.
-    if (!is_object($entity = $request->attributes->get('_converted_entity'))) {
-      $entity_id = $entity;
+    if (!$request->attributes->get('converted')->get('entity')) {
+      $entity_id = $request->attributes->get('entity');
       $entity_type = $request->attributes->get('entity_type');
       if (!$entity_type || !entity_get_info($entity_type)) {
         throw new NotFoundHttpException();
@@ -60,8 +60,7 @@ protected function validateAndUpcastRequestAttributes(Request $request) {
       if (!$entity) {
         throw new NotFoundHttpException();
       }
-      // @todo Why does the field access check converts the parameters.
-      $request->attributes->set('_converted_entity', $entity);
+      $request->attributes->get('converted')->set('entity', $entity);
     }
 
     // Validate the field name and language.
diff --git a/core/modules/filter/lib/Drupal/filter/Access/FilterAccessCheck.php b/core/modules/filter/lib/Drupal/filter/Access/FilterAccessCheck.php
index 20c6912..c447147 100644
--- a/core/modules/filter/lib/Drupal/filter/Access/FilterAccessCheck.php
+++ b/core/modules/filter/lib/Drupal/filter/Access/FilterAccessCheck.php
@@ -27,7 +27,7 @@ public function applies(Route $route) {
    * {@inheritdoc}
    */
   public function access(Route $route, Request $request) {
-    if ($format = $request->attributes->get('_converted_filter_format')) {
+    if ($format = $request->attributes->get('converted')->get('filter_format')) {
       // Handle special cases up front. All users have access to the fallback
       // format.
       if ($format->format == filter_fallback_format()) {
diff --git a/core/modules/filter/lib/Drupal/filter/Access/FormatDisableCheck.php b/core/modules/filter/lib/Drupal/filter/Access/FormatDisableCheck.php
index beeaf6f..eab9db2 100644
--- a/core/modules/filter/lib/Drupal/filter/Access/FormatDisableCheck.php
+++ b/core/modules/filter/lib/Drupal/filter/Access/FormatDisableCheck.php
@@ -27,7 +27,7 @@ public function applies(Route $route) {
    * Implements \Drupal\Core\Access\AccessCheckInterface::access().
    */
   public function access(Route $route, Request $request) {
-    if ($format = $request->attributes->get('_converted_filter_format')) {
+    if ($format = $request->attributes->get('converted')->get('filter_format')) {
       return user_access('administer filters') && ($format->format != filter_fallback_format());
     }
 
diff --git a/core/modules/menu/lib/Drupal/menu/Access/DeleteLinkAccessCheck.php b/core/modules/menu/lib/Drupal/menu/Access/DeleteLinkAccessCheck.php
index c1cc60d..4df0d40 100644
--- a/core/modules/menu/lib/Drupal/menu/Access/DeleteLinkAccessCheck.php
+++ b/core/modules/menu/lib/Drupal/menu/Access/DeleteLinkAccessCheck.php
@@ -27,7 +27,7 @@ public function applies(Route $route) {
    * {@inheritdoc}
    */
   public function access(Route $route, Request $request) {
-    if (user_access('administer menu') && $menu_link = $request->attributes->get('_converted_menu_link')) {
+    if (user_access('administer menu') && $menu_link = $request->attributes->get('converted')->get('menu_link')) {
       // Links defined via hook_menu may not be deleted. Updated items are an
       // exception, as they can be broken.
       return $menu_link->module !== 'system' || $menu_link->updated;
diff --git a/core/modules/menu/lib/Drupal/menu/Access/DeleteMenuAccessCheck.php b/core/modules/menu/lib/Drupal/menu/Access/DeleteMenuAccessCheck.php
index 72ebe4d..42c3f6a 100644
--- a/core/modules/menu/lib/Drupal/menu/Access/DeleteMenuAccessCheck.php
+++ b/core/modules/menu/lib/Drupal/menu/Access/DeleteMenuAccessCheck.php
@@ -27,7 +27,7 @@ public function applies(Route $route) {
    * {@inheritdoc}
    */
   public function access(Route $route, Request $request) {
-    if (user_access('administer menu') && $menu = $request->attributes->get('_converted_menu')) {
+    if (user_access('administer menu') && $menu = $request->attributes->get('converted')->get('menu')) {
       // System-defined menus may not be deleted.
       $system_menus = menu_list_system_menus();
       return !isset($system_menus[$menu->id()]);