diff --git a/src/Routing/Routes.php b/src/Routing/Routes.php
index c337813..2ff3c04 100644
--- a/src/Routing/Routes.php
+++ b/src/Routing/Routes.php
@@ -126,8 +126,8 @@ class Routes implements ContainerInjectionInterface {
       ];
 
       // Collection endpoint, like /jsonapi/file/photo.
-      $route_collection = (new Route($route_base_path, $defaults))
-        ->addDefaults(['serialization_class' => JsonApiDocumentTopLevel::class])
+      $route_collection = (new Route($route_base_path))
+        ->addDefaults($defaults + ['serialization_class' => JsonApiDocumentTopLevel::class])
         ->setRequirement('_entity_type', (string) $resource_type->getEntityTypeId())
         ->setRequirement('_bundle', (string) $resource_type->getBundle())
         ->setRequirement('_jsonapi_custom_query_parameter_names', 'TRUE')
@@ -142,8 +142,8 @@ class Routes implements ContainerInjectionInterface {
           'type' => 'entity:' . $resource_type->getEntityTypeId(),
         ],
       ]);
-      $route_individual = (new Route(sprintf('%s/{%s}', $route_base_path, $resource_type->getEntityTypeId()), $defaults))
-        ->addDefaults(['serialization_class' => JsonApiDocumentTopLevel::class])
+      $route_individual = (new Route(sprintf('%s/{%s}', $route_base_path, $resource_type->getEntityTypeId())))
+        ->addDefaults($defaults + ['serialization_class' => JsonApiDocumentTopLevel::class])
         ->setRequirement('_entity_type', (string) $resource_type->getEntityTypeId())
         ->setRequirement('_bundle', (string) $resource_type->getBundle())
         ->setRequirement('_jsonapi_custom_query_parameter_names', 'TRUE')
@@ -154,7 +154,8 @@ class Routes implements ContainerInjectionInterface {
       $collection->add($build_route_name('individual'), $route_individual);
 
       // Related resource, like /jsonapi/file/photo/123/comments.
-      $route_related = (new Route(sprintf('%s/{%s}/{related}', $route_base_path, $resource_type->getEntityTypeId()), $defaults))
+      $route_related = (new Route(sprintf('%s/{%s}/{related}', $route_base_path, $resource_type->getEntityTypeId())))
+        ->addDefaults($defaults)
         ->setRequirement('_entity_type', (string) $resource_type->getEntityTypeId())
         ->setRequirement('_bundle', (string) $resource_type->getBundle())
         ->setRequirement('_jsonapi_custom_query_parameter_names', 'TRUE')
@@ -165,8 +166,13 @@ class Routes implements ContainerInjectionInterface {
       $collection->add($build_route_name('related'), $route_related);
 
       // Related endpoint, like /jsonapi/file/photo/123/relationships/comments.
-      $route_relationship = (new Route(sprintf('%s/{%s}/relationships/{related}', $route_base_path, $resource_type->getEntityTypeId()), $defaults + ['_on_relationship' => TRUE]))
-        ->addDefaults(['serialization_class' => EntityReferenceFieldItemList::class])
+      $route_relationship = (new Route(sprintf('%s/{%s}/relationships/{related}', $route_base_path, $resource_type->getEntityTypeId())))
+        ->addDefaults(
+          $defaults + [
+            '_on_relationship' => TRUE,
+            'serialization_class' => EntityReferenceFieldItemList::class,
+          ]
+        )
         ->setRequirement('_entity_type', (string) $resource_type->getEntityTypeId())
         ->setRequirement('_bundle', (string) $resource_type->getBundle())
         ->setRequirement('_jsonapi_custom_query_parameter_names', 'TRUE')