diff --git a/System/Log/FastLogger/Date.hs b/System/Log/FastLogger/Date.hs
--- a/System/Log/FastLogger/Date.hs
+++ b/System/Log/FastLogger/Date.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE CPP #-}
+{-# LANGUAGE CPP, OverloadedStrings #-}
 
 module System.Log.FastLogger.Date (
     ZonedDate
@@ -9,16 +9,16 @@
 
 import Control.Applicative
 import Data.ByteString (ByteString)
-import qualified Data.ByteString.Char8 as BS
 import Data.IORef
+#if WINDOWS
+import qualified Data.ByteString.Char8 as BS
 import Data.Time
 import System.Locale
-#if WINDOWS
 #define TIME UTCTime
 #define GETTIME getCurrentTime
 #else
+import Data.UnixTime
 import System.Posix (EpochTime, epochTime)
-import Data.Time.Clock.POSIX
 #define TIME EpochTime
 #define GETTIME epochTime
 #endif
@@ -27,9 +27,9 @@
 type ZonedDate = ByteString
 
 data DateCache = DateCache {
-    unixTime :: !TIME
+    timeKey  :: !TIME
   , zonedDate :: !ZonedDate
-  }
+  } deriving (Eq, Show)
 
 -- | Reference to the 'ZonedDate' cache.
 newtype DateRef = DateRef (IORef DateCache)
@@ -39,7 +39,7 @@
 getDate (DateRef ref) = do
     newEt <- GETTIME
     cache <- readIORef ref
-    let oldEt = unixTime cache
+    let oldEt = timeKey cache
     if oldEt == newEt then
         return $ zonedDate cache
       else do
@@ -48,15 +48,16 @@
         return $ zonedDate newCache
 
 newDate :: TIME -> IO DateCache
+#if WINDOWS
 newDate et = DateCache et . format <$> toZonedTime et
   where
-    toZonedTime = utcToLocalZonedTime . toUTC
-#if WINDOWS
-    toUTC = id
+    format = BS.pack . formatTime defaultTimeLocale "%d/%b/%Y:%T %z"
+    toZonedTime = utcToLocalZonedTime
 #else
-    toUTC = posixSecondsToUTCTime . realToFrac
+newDate et = return $ DateCache et $ toZonedTime et
+  where
+    toZonedTime = formatUnixTime "%d/%b/%Y:%T %z" . fromEpochTime
 #endif
-    format = BS.pack . formatTime defaultTimeLocale "%d/%b/%Y:%T %z"
 
 -- | Initializing the 'ZonedDate' cache.
 dateInit :: IO DateRef
diff --git a/fast-logger.cabal b/fast-logger.cabal
--- a/fast-logger.cabal
+++ b/fast-logger.cabal
@@ -1,5 +1,5 @@
 Name:                   fast-logger
-Version:                0.2.0
+Version:                0.2.1
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3
@@ -19,13 +19,14 @@
                       , bytestring
                       , directory
                       , filepath
-                      , old-locale
                       , text
-                      , time
   if os(windows)
-    cpp-options: -DWINDOWS
+    Cpp-Options:        -DWINDOWS
+    Build-Depends:      old-locale
+                      , time
   else
-    build-depends: unix
+    Build-Depends:      unix
+                      , unix-time
 Source-Repository head
   Type:                 git
   Location:             git://github.com/kazu-yamamoto/logger.git