diff --git a/config/routes.rb b/config/routes.rb
index c11b78ba2..7aec1655a 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -273,7 +273,7 @@ Rails.application.routes.draw do
       end
     end
 
-    resources :instances, only: [:index, :show, :destroy], constraints: { id: /[^\/]+/ } do
+    resources :instances, only: [:index, :show, :destroy], constraints: { id: /[^\/]+/ }, format: 'html' do
       member do
         post :clear_delivery_errors
         post :restart_delivery