diff --git a/core/lib/Drupal/Core/Access/AccessArgumentsResolverFactory.php b/core/lib/Drupal/Core/Access/AccessArgumentsResolverFactory.php
index cdef380..ddb3a51 100644
--- a/core/lib/Drupal/Core/Access/AccessArgumentsResolverFactory.php
+++ b/core/lib/Drupal/Core/Access/AccessArgumentsResolverFactory.php
@@ -22,11 +22,7 @@ class AccessArgumentsResolverFactory implements AccessArgumentsResolverFactoryIn
    */
   public function getArgumentsResolver(RouteMatchInterface $route_match, AccountInterface $account, Request $request = NULL) {
     $route = $route_match->getRouteObject();
-
-    // Defaults for the parameters defined on the route object need to be added
-    // to the raw arguments.
-    $raw_route_arguments = $route_match->getRawParameters()->all() + $route->getDefaults();
-
+    $raw_route_arguments = $route_match->getRawParameters()->all();
     $upcasted_route_arguments = $route_match->getParameters()->all();
 
     // Parameters which are not defined on the route object, but still are
diff --git a/core/lib/Drupal/Core/Access/AccessManager.php b/core/lib/Drupal/Core/Access/AccessManager.php
index 5b2f871..b919c62 100644
--- a/core/lib/Drupal/Core/Access/AccessManager.php
+++ b/core/lib/Drupal/Core/Access/AccessManager.php
@@ -168,7 +168,7 @@ public function checkNamedRoute($route_name, array $parameters, AccountInterface
       // ParamConverterManager relies on the route object being available
       // from the parameters array.
       $parameters[RouteObjectInterface::ROUTE_OBJECT] = $route;
-      $upcasted_parameters = $this->paramConverterManager->convert($parameters, new Request());
+      $upcasted_parameters = $this->paramConverterManager->convert($parameters + $route->getDefaults(), new Request());
 
       $route_match = new RouteMatch($route_name, $route, $upcasted_parameters, $parameters);
       return $this->check($route_match, $account);