diff --git a/config/routes.rb b/config/routes.rb
index 49c00253646..f5eccd9af5e 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -828,7 +828,7 @@ Discourse::Application.routes.draw do
 
     # Topic routes
     get "t/id_for/:slug" => "topics#id_for_slug"
-    get "t/external_id/:external_id" => "topics#show_by_external_id", format: :json, constrains: { external_id: /\A[\w-]+\z/ }
+    get "t/external_id/:external_id" => "topics#show_by_external_id", format: :json, constraints: { external_id: /[\w-]+/ }
     get "t/:slug/:topic_id/print" => "topics#show", format: :html, print: 'true', constraints: { topic_id: /\d+/ }
     get "t/:slug/:topic_id/wordpress" => "topics#wordpress", constraints: { topic_id: /\d+/ }
     get "t/:topic_id/wordpress" => "topics#wordpress", constraints: { topic_id: /\d+/ }