diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index dee4516fbeff70cf280e11c829896cc5cd0ea0fd..ae4470d0336beee494b6334a62633f7bad3f1e94 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/hash/except'
+
 module ActionDispatch
   module Routing
     class Mapper