again, use Set#subtract

1 files changed, 1 insertions, 1 deletions

diff --git a/actionpack/lib/action_dispatch/middleware/flash.rb b/actionpack/lib/action_dispatch/middleware/flash.rb
index e79050706d..d1545355f8 100644
--- a/actionpack/lib/action_dispatch/middleware/flash.rb
+++ b/actionpack/lib/action_dispatch/middleware/flash.rb
@@ -190,7 +190,7 @@ module ActionDispatch
         end
 
         # clean up after keys that could have been left over by calling reject! or shift on the flash
-        (@used - keys).each{ |k| @used.delete(k) }
+        @used.subtract(@used - keys)
       end
 
       # Convenience accessor for flash[:alert]