diff --git a/servant-server/src/Servant/Server.hs b/servant-server/src/Servant/Server.hs
index 58c34ea3..2a886683 100644
--- a/servant-server/src/Servant/Server.hs
+++ b/servant-server/src/Servant/Server.hs
@@ -33,7 +33,7 @@ module Servant.Server
   , embedNat
   , squashNat
   , generalizeNat
-
+  , tweakResponse
 
     -- * Default error type
   , ServantErr(..)
diff --git a/servant-server/src/Servant/Server/Internal/Router.hs b/servant-server/src/Servant/Server/Internal/Router.hs
index f188955e..89f7c144 100644
--- a/servant-server/src/Servant/Server/Internal/Router.hs
+++ b/servant-server/src/Servant/Server/Internal/Router.hs
@@ -1,25 +1,34 @@
+{-# LANGUAGE DeriveFunctor #-}
+
 module Servant.Server.Internal.Router where
 
 import           Data.Map                                   (Map)
 import qualified Data.Map                                   as M
 import           Data.Monoid                                ((<>))
 import           Data.Text                                  (Text)
-import           Network.Wai                                (Request, pathInfo)
+import           Network.Wai                                (Request, Response, pathInfo)
 import           Servant.Server.Internal.PathInfo
 import           Servant.Server.Internal.RoutingApplication
 
+type Router = Router' RoutingApplication
+
 -- | Internal representation of a router.
-data Router =
+data Router' a =
     WithRequest   (Request -> Router)
       -- ^ current request is passed to the router
   | StaticRouter  (Map Text Router)
       -- ^ first path component used for lookup and removed afterwards
   | DynamicRouter (Text -> Router)
       -- ^ first path component used for lookup and removed afterwards
-  | LeafRouter    RoutingApplication
+  | LeafRouter    a
       -- ^ to be used for routes that match an empty path
   | Choice        Router Router
       -- ^ left-biased choice between two routers
+  deriving Functor
+
+-- | Apply a transformation to the response of a `Router`.
+tweakResponse :: (RouteResult Response -> RouteResult Response) -> Router -> Router
+tweakResponse f = fmap (\a -> \req cont -> a req (cont . f))
 
 -- | Smart constructor for the choice between routers.
 -- We currently optimize the following cases:
@@ -69,4 +78,3 @@ runRouter (Choice r1 r2)       request respond =
       then runRouter r2 request $ \ mResponse2 ->
              respond (mResponse1 <> mResponse2)
       else respond mResponse1
-
diff --git a/servant-server/test/Servant/ServerSpec.hs b/servant-server/test/Servant/ServerSpec.hs
index 45519e42..9c7e85c3 100644
--- a/servant-server/test/Servant/ServerSpec.hs
+++ b/servant-server/test/Servant/ServerSpec.hs
@@ -1,14 +1,17 @@
-{-# LANGUAGE DataKinds           #-}
-{-# LANGUAGE DeriveGeneric       #-}
-{-# LANGUAGE OverloadedStrings   #-}
-{-# LANGUAGE ScopedTypeVariables #-}
-{-# LANGUAGE TypeOperators       #-}
-{-# LANGUAGE TypeSynonymInstances       #-}
-{-# LANGUAGE FlexibleInstances       #-}
+{-# LANGUAGE CPP                  #-}
+{-# LANGUAGE DataKinds            #-}
+{-# LANGUAGE DeriveGeneric        #-}
+{-# LANGUAGE OverloadedStrings    #-}
+{-# LANGUAGE ScopedTypeVariables  #-}
+{-# LANGUAGE TypeOperators        #-}
+{-# LANGUAGE TypeSynonymInstances #-}
+{-# LANGUAGE FlexibleInstances    #-}
 
 module Servant.ServerSpec where
 
-
+#if !MIN_VERSION_base(4,8,0)
+import           Control.Applicative        ((<$>))
+#endif
 import           Control.Monad              (forM_, when)
 import           Control.Monad.Trans.Except (ExceptT, throwE)
 import           Data.Aeson                 (FromJSON, ToJSON, decode', encode)
@@ -23,10 +26,12 @@ import           GHC.Generics               (Generic)
 import           Network.HTTP.Types         (hAccept, hContentType,
                                              methodDelete, methodGet, methodHead,
                                              methodPatch, methodPost, methodPut,
-                                             ok200, parseQuery, status409)
+                                             ok200, parseQuery, status409,
+                                             Status(..))
 import           Network.Wai                (Application, Request, pathInfo,
                                              queryString, rawQueryString,
-                                             responseLBS)
+                                             responseLBS, responseBuilder)
+import           Network.Wai.Internal       (Response(ResponseBuilder))
 import           Network.Wai.Test           (defaultRequest, request,
                                              runSession, simpleBody)
 import           Test.Hspec                 (Spec, describe, it, shouldBe)
@@ -41,8 +46,12 @@ import           Servant.API                ((:<|>) (..), (:>),
                                              Post, Put, RemoteHost, QueryFlag, QueryParam,
                                              QueryParams, Raw, ReqBody)
 import           Servant.Server             (Server, serve, ServantErr(..), err404)
+import           Servant.Server.Internal.Router
+                                            (tweakResponse, runRouter,
+                                             Router, Router'(LeafRouter))
 import           Servant.Server.Internal.RoutingApplication
-                                            (RouteMismatch (..))
+                                            (RouteResult(..), RouteMismatch(..),
+                                             toApplication)
 
 
 -- * test data types
@@ -92,6 +101,7 @@ spec = do
   unionSpec
   prioErrorsSpec
   errorsSpec
+  routerSpec
   responseHeadersSpec
   miscReqCombinatorsSpec
 
@@ -697,6 +707,24 @@ errorsSpec = do
       nf <> ib `shouldBe` ib
       nf <> wm `shouldBe` wm
 
+routerSpec :: Spec
+routerSpec = do
+  describe "Servant.Server.Internal.Router" $ do
+    let app' :: Application
+        app' = toApplication $ runRouter router'
+
+        router', router :: Router
+        router' = tweakResponse (twk <$>) router
+        router = LeafRouter $ \_ cont -> cont (RR . Right $ responseBuilder (Status 201 "") [] "")
+
+        twk :: Response -> Response
+        twk (ResponseBuilder (Status i s) hs b) = ResponseBuilder (Status (i + 1) s) hs b
+        twk b = b
+
+    describe "tweakResponse" . with (return app') $ do
+      it "calls f on route result" $ do
+        get "" `shouldRespondWith` 202
+
 type MiscCombinatorsAPI
   =    "version" :> HttpVersion :> Get '[JSON] String
   :<|> "secure"  :> IsSecure :> Get '[JSON] String