diff --git a/config/environments/production.rb b/config/environments/production.rb
index 88ae2d6a712..b3bb90c4140 100644
--- a/config/environments/production.rb
+++ b/config/environments/production.rb
@@ -188,6 +188,9 @@ Rails.application.configure do
         base = OpenProject::Configuration["rails_relative_url_root"]
         request.path.start_with?("#{base}/health_check") ||
           request.path.start_with?("#{base}/sys")
+      end,
+      response_app: -> env do
+        [400, { "Content-Type" => "text/plain" }, ["Invalid host_name configuration"]]
       end
     }
   end