diff --git a/config/routes.rb b/config/routes.rb
index 730d43cf..70b850b7 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -1,6 +1,8 @@
 Osem::Application.routes.draw do
-  mount LetterOpenerWeb::Engine, at: '/letter_opener' if Rails.env.development?
-
+  if Rails.env.development? && defined?(LetterOpenerWeb)
+    mount LetterOpenerWeb::Engine, at: '/letter_opener'
+  end
+  
   constraints DomainConstraint do
     get '/', to: 'conferences#show'
   end