diff --git a/Yesod/Request.hs b/Yesod/Request.hs
index 1c455faa..589aaeb8 100644
--- a/Yesod/Request.hs
+++ b/Yesod/Request.hs
@@ -29,9 +29,9 @@ module Yesod.Request
     , languages
     , parseWaiRequest
       -- * Parameter
-    , ParamType (..)
     , ParamName
     , ParamValue
+    , ParamError
 #if TEST
     , testSuite
 #endif
@@ -56,9 +56,9 @@ import Test.Framework (testGroup, Test)
 --import Test.HUnit hiding (Test)
 #endif
 
-data ParamType = GetParam | PostParam
 type ParamName = String
 type ParamValue = String
+type ParamError = String
 
 class RequestReader m where
     getRawRequest :: m RawRequest
diff --git a/Yesod/Response.hs b/Yesod/Response.hs
index 6c5a5726..085cc6b2 100644
--- a/Yesod/Response.hs
+++ b/Yesod/Response.hs
@@ -65,6 +65,7 @@ import qualified Data.Text.Lazy.Encoding as DTLE
 import Web.Encodings (formatW3)
 import qualified Network.Wai as W
 import qualified Network.Wai.Enumerator as WE
+import Yesod.Request
 
 #if TEST
 import Data.Object.Html hiding (testSuite)
@@ -192,7 +193,7 @@ data SpecialResponse =
 data ErrorResponse =
       NotFound
     | InternalError String
-    | InvalidArgs [(String, String)] -- FIXME use SomeException?
+    | InvalidArgs [(ParamName, ParamError)]
     | PermissionDenied
     deriving (Show, Eq)