diff --git a/actionpack/lib/action_dispatch/middleware/flash.rb b/actionpack/lib/action_dispatch/middleware/flash.rb
index 419bcb8a7378ef60a6faed85df0cdeaf7ffdb89a..1e45a38e5f9e29518c2b80cc1a12ad7b53a31b71 100644
--- a/actionpack/lib/action_dispatch/middleware/flash.rb
+++ b/actionpack/lib/action_dispatch/middleware/flash.rb
@@ -1,3 +1,5 @@
+require 'active_support/core_ext/hash/keys'
+
 module ActionDispatch
   class Request < Rack::Request
     # Access the contents of the flash. Use <tt>flash["notice"]</tt> to
@@ -94,7 +96,7 @@ def to_session_value
 
       def initialize(flashes = {}, discard = []) #:nodoc:
         @discard = Set.new(stringify_array(discard))
-        @flashes = flashes
+        @flashes = flashes.stringify_keys
         @now     = nil
       end