diff --git a/haskell/msgpack.cabal b/haskell/msgpack.cabal
index 3baff77f..bd10c4aa 100644
--- a/haskell/msgpack.cabal
+++ b/haskell/msgpack.cabal
@@ -24,7 +24,9 @@ Library
                     iteratee >= 0.4 && < 0.5,
                     attoparsec >= 0.8.1 && < 0.8.2,
                     binary >= 0.5.0 && < 0.5.1,
-                    data-binary-ieee754 >= 0.4 && < 0.5
+                    data-binary-ieee754 >= 0.4 && < 0.5,
+                    deepseq >= 1.1 && <1.2
+
   Ghc-options:      -Wall -O2
   Hs-source-dirs:   src
 
diff --git a/haskell/src/Data/MessagePack/Object.hs b/haskell/src/Data/MessagePack/Object.hs
index df0e89dd..6806722b 100644
--- a/haskell/src/Data/MessagePack/Object.hs
+++ b/haskell/src/Data/MessagePack/Object.hs
@@ -25,6 +25,7 @@ module Data.MessagePack.Object(
   Result,
   ) where
 
+import Control.DeepSeq
 import Control.Monad
 import Control.Monad.Trans.Error ()
 import qualified Data.ByteString as B
@@ -41,6 +42,17 @@ data Object =
   | ObjectMap [(Object, Object)]
   deriving (Show)
 
+instance NFData Object where
+  rnf obj =
+    case obj of
+      ObjectNil -> ()
+      ObjectBool b -> rnf b
+      ObjectInteger n -> rnf n
+      ObjectDouble d -> rnf d
+      ObjectRAW bs -> bs `seq` ()
+      ObjectArray a -> rnf a
+      ObjectMap m -> rnf m
+
 -- | The class of types serializable to and from MessagePack object
 class OBJECT a where
   -- | Encode a value to MessagePack object