diff --git a/Yesod/Core.hs b/Yesod/Core.hs
index 00d0b0b6..82ef97df 100644
--- a/Yesod/Core.hs
+++ b/Yesod/Core.hs
@@ -179,9 +179,9 @@ class RenderRoute (Route a) => Yesod a where
     authRoute :: a -> Maybe (Route a)
     authRoute _ = Nothing
 
-    -- | A function used to clean up path segments. It returns 'Nothing' when
-    -- the given path is already clean, and a 'Just' when Yesod should redirect
-    -- to the given path pieces.
+    -- | A function used to clean up path segments. It returns 'Right' with a
+    -- clean path or 'Left' with a new set of pieces the user should be
+    -- redirected to. The default implementation enforces:
     --
     -- * No double slashes
     --
@@ -189,11 +189,11 @@ class RenderRoute (Route a) => Yesod a where
     --
     -- Note that versions of Yesod prior to 0.7 used a different set of rules
     -- involing trailing slashes.
-    cleanPath :: a -> [String] -> Maybe [String]
+    cleanPath :: a -> [String] -> Either [String] [String]
     cleanPath _ s =
         if corrected == s
-            then Nothing
-            else Just corrected
+            then Right s
+            else Left corrected
       where
         corrected = filter (not . null) s
 
diff --git a/Yesod/Dispatch.hs b/Yesod/Dispatch.hs
index 096ebf02..43c30b21 100644
--- a/Yesod/Dispatch.hs
+++ b/Yesod/Dispatch.hs
@@ -189,11 +189,11 @@ toWaiApp' y key' env = do
         Just app -> app env
         Nothing ->
             case cleanPath y segments of
-                Nothing ->
-                    case yesodDispatch y key' segments y id of
+                Right segments' ->
+                    case yesodDispatch y key' segments' y id of
                         Just app -> app env
                         Nothing -> yesodRunner y y id key' Nothing notFound env
-                Just segments' ->
+                Left segments' ->
                     let dest = joinPath y (approot y) segments' []
                         dest' =
                             if S.null (W.queryString env)