diff --git a/bytable.cabal b/bytable.cabal
--- a/bytable.cabal
+++ b/bytable.cabal
@@ -2,7 +2,7 @@
 build-type:	Simple
 
 name:		bytable
-version:	0.0.0.8
+version:	0.0.0.9
 stability:	Experimental
 author:		Yoshikuni Jujo <PAF01143@nifty.ne.jp>
 maintainer:	Yoshikuni Jujo <PAF01143@nifty.ne.jp>
@@ -28,7 +28,7 @@
 source-repository	this
     type:	git
     location:	git://github.com/YoshikuniJujo/forest
-    tag:	bytable-0.0.0.8
+    tag:	bytable-0.0.0.9
 
 library
     hs-source-dirs:	src
diff --git a/src/Codec/Bytable.hs b/src/Codec/Bytable.hs
--- a/src/Codec/Bytable.hs
+++ b/src/Codec/Bytable.hs
@@ -1,10 +1,10 @@
-{-# LANGUAGE TupleSections #-}
+{-# LANGUAGE PatternGuards, OverloadedStrings, TupleSections #-}
 
 module Codec.Bytable (
 	Bytable(..),
 	Parsable(..),
 	BytableM(..), evalBytableM, execBytableM,
-	head, take, null, list, addLength,
+	head, take, null, list, addLen,
 ) where
 
 import Prelude hiding (take, head, null)
@@ -40,6 +40,13 @@
 	fromByteString :: BS.ByteString -> Either String b
 	toByteString :: b -> BS.ByteString
 
+instance Bytable Word8 where
+	fromByteString "" = Right 0
+	fromByteString bs
+		| [w] <- BS.unpack bs = Right w
+	fromByteString _ = Left "Codec.Bytable.BigEndian: Bytable Word8: too large"
+	toByteString = BS.pack . (: [])
+
 instance Bytable BS.ByteString where
 	fromByteString = Right
 	toByteString = id
@@ -73,6 +80,6 @@
 		e <- null
 		if e then return [] else (:) <$> m <*> lst
 
-addLength :: (Bytable n, Num n) => n -> BS.ByteString -> BS.ByteString
-addLength t bs =
+addLen :: (Bytable n, Num n) => n -> BS.ByteString -> BS.ByteString
+addLen t bs =
 	toByteString (fromIntegral (BS.length bs) `asTypeOf` t) `BS.append` bs
diff --git a/src/Codec/Bytable/BigEndian.hs b/src/Codec/Bytable/BigEndian.hs
--- a/src/Codec/Bytable/BigEndian.hs
+++ b/src/Codec/Bytable/BigEndian.hs
@@ -19,13 +19,6 @@
 	fromByteString bs = Right $ byteStringToNum bs
 	toByteString = integralToByteString
 
-instance Bytable Word8 where
-	fromByteString bs
-		| BS.length bs <= 1 = Right $ byteStringToNum bs
-		| otherwise = Left
-			"Codec.Bytable.BigEndian: Bytable Word8: too large"
-	toByteString = integralToByteStringN 1
-
 instance Bytable Word16 where
 	fromByteString bs
 		| BS.length bs <= 2 = Right $ byteStringToNum bs