diff --git a/core/core.services.yml b/core/core.services.yml
index 5bfe41b..bdc9516 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -179,7 +179,7 @@ services:
     class: Drupal\Core\Theme\AjaxBasePageNegotiator
     arguments: ['@csrf_token']
     tags:
-      - { name: theme_negotiator }
+      - { name: theme_negotiator, priority: 1000 }
   container.namespaces:
     class: ArrayObject
     arguments: [ '%container.namespaces%' ]
diff --git a/core/modules/block/block.services.yml b/core/modules/block/block.services.yml
index d84e45d..29a31c2 100644
--- a/core/modules/block/block.services.yml
+++ b/core/modules/block/block.services.yml
@@ -12,5 +12,5 @@ services:
   theme.negotiator.block.admin_demo:
     class: Drupal\block\Theme\AdminDemoNegotiator
     tags:
-      - { name: theme_negotiator }
+      - { name: theme_negotiator, priority: 1000 }
 
diff --git a/core/modules/system/system.services.yml b/core/modules/system/system.services.yml
index 079b44d..99faa25 100644
--- a/core/modules/system/system.services.yml
+++ b/core/modules/system/system.services.yml
@@ -23,7 +23,7 @@ services:
     class: Drupal\system\Theme\BatchNegotiator
     arguments: ['@batch.storage']
     tags:
-      - { name: theme_negotiator }
+      - { name: theme_negotiator, priority: 1000 }
   theme.negotiator.admin_theme:
     class: Drupal\system\Theme\AdminNegotiator
     arguments: ['@current_user', '@config.factory', '@entity.manager']