diff --git a/Network/HTTP/Date/Formatter.hs b/Network/HTTP/Date/Formatter.hs
--- a/Network/HTTP/Date/Formatter.hs
+++ b/Network/HTTP/Date/Formatter.hs
@@ -20,12 +20,12 @@
 formatHTTPDate :: HTTPDate -> ByteString
 formatHTTPDate hd =
     unsafeCreate 29 $ \ptr -> do
-        cpy3 ptr weekDays (3 * (w - 1))
+        cpy3 ptr weekDays (3 * w)
         poke (ptr `plusPtr`  3) comma
         poke (ptr `plusPtr`  4) spc
         int2 (ptr `plusPtr`  5) d
         poke (ptr `plusPtr`  7) spc
-        cpy3 (ptr `plusPtr`  8) months (3 * (m - 1))
+        cpy3 (ptr `plusPtr`  8) months (3 * m)
         poke (ptr `plusPtr` 11) spc
         int4 (ptr `plusPtr` 12) y
         poke (ptr `plusPtr` 16) spc
@@ -77,10 +77,10 @@
 ----------------------------------------------------------------
 
 months :: ForeignPtr Word8
-months = let (PS p _ _) = "JanFebMarAprMayJunJulAugSepOctNovDec" in p
+months = let (PS p _ _) = "___JanFebMarAprMayJunJulAugSepOctNovDec" in p
 
 weekDays :: ForeignPtr Word8
-weekDays = let (PS p _ _) = "MonTueWedThuFriSatSun" in p
+weekDays = let (PS p _ _) = "___MonTueWedThuFriSatSun" in p
 
 ----------------------------------------------------------------
 
diff --git a/Network/HTTP/Date/Parser.hs b/Network/HTTP/Date/Parser.hs
--- a/Network/HTTP/Date/Parser.hs
+++ b/Network/HTTP/Date/Parser.hs
@@ -4,8 +4,8 @@
 
 import Control.Applicative
 import Control.Monad
-import Data.Attoparsec
-import Data.Attoparsec.Char8
+import Data.Attoparsec.ByteString
+import Data.Attoparsec.ByteString.Char8
 import Data.ByteString
 import Data.Char
 import Network.HTTP.Date.Types
diff --git a/Network/HTTP/Date/Types.hs b/Network/HTTP/Date/Types.hs
--- a/Network/HTTP/Date/Types.hs
+++ b/Network/HTTP/Date/Types.hs
@@ -22,7 +22,7 @@
   , hdMinute :: !Int
   , hdSecond :: !Int
   , hdWkday  :: !Int
-  } deriving (Eq,Show, Ord)
+  } deriving (Eq, Show, Ord)
 
 {-|
   A default value for 'HTTPDate'.
diff --git a/http-date.cabal b/http-date.cabal
--- a/http-date.cabal
+++ b/http-date.cabal
@@ -1,5 +1,5 @@
 Name:                   http-date
-Version:                0.0.4
+Version:                0.0.5
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3