diff --git a/msgpack-rpc.cabal b/msgpack-rpc.cabal
--- a/msgpack-rpc.cabal
+++ b/msgpack-rpc.cabal
@@ -1,5 +1,5 @@
 Name:                msgpack-rpc
-Version:             0.3.1.3
+Version:             0.4.0
 Synopsis:            A MessagePack-RPC Implementation
 Description:
   A MessagePack-RPC Implementation <http://msgpack.org/>
@@ -11,20 +11,24 @@
 Author:              Hideyuki Tanaka
 Maintainer:          Hideyuki Tanaka <tanaka.hideyuki@gmail.com>
 Homepage:            http://github.com/msgpack/msgpack-rpc
-Stability:	     Experimental
+Stability:	      Experimental
 Cabal-version:       >=1.6
 Build-type:          Simple
 
+Extra-source-files:
+  test/Serv.hs
+  test/Cli.hs
+
 Library
   Build-depends:     base >= 4 && <5,
-                     msgpack >= 0.3.1 && < 0.4,
+                     msgpack >= 0.4.0 && < 0.5,
                      network >= 2.2.1.7 && < 2.2.2,
                      random >= 1.0.0.2 && < 1.1,
                      transformers >= 0.2.1 && < 0.2.2,
                      iteratee >= 0.4.0.2 && < 0.4.1,
                      deepseq >= 1.1 && < 1.2
 
-  Ghc-options:	     -Wall
+  Ghc-options:       -Wall
   Hs-source-dirs:    src
 
   Exposed-modules:
diff --git a/src/Network/MessagePackRpc/Client.hs b/src/Network/MessagePackRpc/Client.hs
--- a/src/Network/MessagePackRpc/Client.hs
+++ b/src/Network/MessagePackRpc/Client.hs
@@ -92,7 +92,7 @@
 
 fromObject' :: OBJECT o => Object -> o
 fromObject' o =
-  case fromObject o of
+  case tryFromObject o of
     Left err -> throw $ ResultTypeError err
     Right r -> r
 
@@ -112,7 +112,7 @@
       throw $ ProtocolError $ "response type is not 1 (got " ++ show rtype ++ ")"
     when (rmsgid /= msgid) $
       throw $ ProtocolError $ "message id mismatch: expect " ++ show msgid ++ ", but got " ++ show rmsgid
-    case fromObject rerror of
+    case tryFromObject rerror of
       Left _ ->
         throw $ ServerError rerror
       Right () ->
diff --git a/src/Network/MessagePackRpc/Server.hs b/src/Network/MessagePackRpc/Server.hs
--- a/src/Network/MessagePackRpc/Server.hs
+++ b/src/Network/MessagePackRpc/Server.hs
@@ -60,7 +60,7 @@
 
 fromObject' :: OBJECT o => Object -> o
 fromObject' o =
-  case fromObject o of
+  case tryFromObject o of
     Left err -> error $ "argument type error: " ++ err
     Right r -> r
 
diff --git a/test/Cli.hs b/test/Cli.hs
new file mode 100644
--- /dev/null
+++ b/test/Cli.hs
@@ -0,0 +1,17 @@
+import Network.MessagePackRpc.Client
+
+import Control.Concurrent
+import Control.Monad
+
+add :: RpcMethod (Int -> Int -> IO Int)
+add  = method "add"
+
+echo :: RpcMethod (String -> IO String)
+echo = method "echo"
+
+main :: IO ()
+main = do
+  conn <- connect "127.0.0.1" 8081
+  forM_ [0..10000] $ \i -> do
+    print =<< add conn i (i*2)
+    print =<< add conn (i*2) (i*3)
diff --git a/test/Serv.hs b/test/Serv.hs
new file mode 100644
--- /dev/null
+++ b/test/Serv.hs
@@ -0,0 +1,11 @@
+import Network.MessagePackRpc.Server
+
+add :: Int -> Int -> IO Int
+add x y = return $ x+y
+
+echo :: String -> IO String
+echo s = return s
+
+main :: IO ()
+main = do
+  serve 8081 [ ("add", fun add), ("echo", fun echo) ]