diff --git a/core/core.services.yml b/core/core.services.yml
index 250e387..106837a 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -268,11 +268,13 @@ services:
     arguments: ['@content_negotiation']
     tags:
       - { name: route_enhancer, priority: 30 }
+      - { name: legacy_route_enhancer, priority: 30 }
   route_enhancer.modal:
     class: Drupal\Core\Routing\Enhancer\ModalEnhancer
     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']
diff --git a/core/lib/Drupal/Core/Routing/Enhancer/DialogEnhancer.php b/core/lib/Drupal/Core/Routing/Enhancer/DialogEnhancer.php
index 8a710a8..32bf977 100644
--- a/core/lib/Drupal/Core/Routing/Enhancer/DialogEnhancer.php
+++ b/core/lib/Drupal/Core/Routing/Enhancer/DialogEnhancer.php
@@ -52,7 +52,7 @@ public function __construct(ContentNegotiation $negotiation) {
    */
   public function enhance(array $defaults, Request $request) {
     if ($this->negotiation->getContentType($request) == $this->targetContentType) {
-      if (empty($defaults['_content']) && !empty($defaults['controller'])) {
+      if (empty($defaults['_content']) && !empty($defaults['_controller'])) {
         // Pass the controller on as content.
         $defaults['_content'] = $defaults['_controller'];
       }