Ruby 1.9.1 requires hash given to foormat to contain symbols.

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -205,7 +205,7 @@ def redirect(*args, &block)
           lambda do |env|
             req = Request.new(env)
 
-            uri = URI.parse(path_proc.call(req.params))
+            uri = URI.parse(path_proc.call(req.params.symbolize_keys))
             uri.scheme ||= req.scheme
             uri.host   ||= req.host
             uri.port   ||= req.port unless req.port == 80