diff --git a/json-rpc-generic.cabal b/json-rpc-generic.cabal
--- a/json-rpc-generic.cabal
+++ b/json-rpc-generic.cabal
@@ -1,5 +1,5 @@
 name:                json-rpc-generic
-version:             0.2.0.2
+version:             0.2.1.0
 synopsis:            Generic encoder and decode for JSON-RPC
 description:         This package contains generic encoder and decode for JSON-RPC
 homepage:            http://github.com/khibino/haskell-json-rpc-generic
diff --git a/src/Data/JsonRpc/Failure.hs b/src/Data/JsonRpc/Failure.hs
--- a/src/Data/JsonRpc/Failure.hs
+++ b/src/Data/JsonRpc/Failure.hs
@@ -3,7 +3,7 @@
 
 module Data.JsonRpc.Failure (
   Failure (..), Error (..),
-  ErrorStatus (..), toCode, fromCode,
+  ErrorStatus (..), toCode, fromCode, refineStatus,
 
   failure, makeError,
   serverError,
@@ -100,6 +100,14 @@
   | otherwise    =  serverError c `mplus` methodError c
   where
     c = toInteger c'
+
+refineStatus :: MonadPlus m
+             => ErrorStatus
+             -> m ErrorStatus
+refineStatus e = do
+  e' <- fromCode $ toCode e
+  guard $ e' == e
+  return e
 
 makeError :: ErrorStatus -> Maybe Text -> Maybe e -> Error e
 makeError e = Error e . fromMaybe (defaultMessage e)
diff --git a/test/Iso.hs b/test/Iso.hs
--- a/test/Iso.hs
+++ b/test/Iso.hs
@@ -15,6 +15,10 @@
 errorStatusCode s =
  Error.fromCode (Error.toCode s) == Just s
 
+refineStatus :: ErrorStatus -> Bool
+refineStatus s =
+  Error.refineStatus s == Just s
+
 aesonED :: (Eq a, ToJSON a, FromJSON a)
         => a -> Bool
 aesonED x = Aeson.decode (Aeson.encode x) == Just x
@@ -38,6 +42,7 @@
 tests :: [Test]
 tests =
   [ qcTest "iso - error status code"  errorStatusCode
+  , qcTest "iso - refine status"  refineStatus
   ] ++
 
   [ x