diff --git a/Data/UnixTime/Types.hs b/Data/UnixTime/Types.hs
--- a/Data/UnixTime/Types.hs
+++ b/Data/UnixTime/Types.hs
@@ -8,13 +8,14 @@
 -- | Data structure for Unix time.
 data UnixTime = UnixTime {
   -- | Seconds from 1st Jan 1970
-    utSeconds :: !CTime
+    utSeconds :: {-# UNPACK #-} !CTime
   -- | Micro seconds (i.e. 10^(-6))
-  , utMicroSeconds :: !Int32
+  , utMicroSeconds :: {-# UNPACK #-} !Int32
   } deriving (Eq,Ord,Show)
 
 -- | Format of the strptime()/strftime() style.
 type Format = ByteString
 
 -- | Data structure for UnixTime diff.
-data UnixDiffTime = UnixDiffTime !CTime !Int32 deriving (Eq,Ord,Show)
+data UnixDiffTime = UnixDiffTime {-# UNPACK #-} !CTime
+                                 {-# UNPACK #-} !Int32 deriving (Eq,Ord,Show)
diff --git a/unix-time.cabal b/unix-time.cabal
--- a/unix-time.cabal
+++ b/unix-time.cabal
@@ -1,5 +1,5 @@
 Name:                   unix-time
-Version:                0.0.1
+Version:                0.0.2
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3