diff -u b/core/core.services.yml b/core/core.services.yml
--- b/core/core.services.yml
+++ b/core/core.services.yml
@@ -254,6 +254,7 @@
     arguments: ['@content_negotiation']
     tags:
       - { name: route_enhancer, priority: 20 }
+      - { name: legacy_route_enhancer, priority: 20 }
   route_enhancer.form:
     class: Drupal\Core\Routing\Enhancer\FormEnhancer
     arguments: ['@content_negotiation']
only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/DependencyInjection/Compiler/RegisterRouteEnhancersPass.php
+++ b/core/lib/Drupal/Core/DependencyInjection/Compiler/RegisterRouteEnhancersPass.php
@@ -28,11 +28,15 @@ public function process(ContainerBuilder $container) {
     }
 
     $router = $container->getDefinition('router.dynamic');
-
-    $services = array();
     foreach ($container->findTaggedServiceIds('route_enhancer') as $id => $attributes) {
       $priority = isset($attributes[0]['priority']) ? $attributes[0]['priority'] : 0;
       $router->addMethodCall('addRouteEnhancer', array(new Reference($id), $priority));
     }
+
+    $legacy_router = $container->getDefinition('legacy_router');
+    foreach ($container->findTaggedServiceIds('legacy_route_enhancer') as $id => $attributes) {
+      $priority = isset($attributes[0]['priority']) ? $attributes[0]['priority'] : 0;
+      $legacy_router->addMethodCall('addRouteEnhancer', array(new Reference($id), $priority));
+    }
   }
 }