diff --git a/Data/Hex.hs b/Data/Hex.hs
--- a/Data/Hex.hs
+++ b/Data/Hex.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE TypeSynonymInstances #-}
 -----------------------------------------------------------------------------
 -- |
@@ -13,7 +14,7 @@
 -----------------------------------------------------------------------------
 module Data.Hex(Hex(..)) where
 
-import Control.Monad
+import Control.Monad (liftM)
 import qualified Data.ByteString.Char8 as B
 import qualified Data.ByteString.Lazy.Char8 as L
 
@@ -22,8 +23,10 @@
     -- | Convert string into hexadecimal.
     hex   :: t -> t
     -- | Convert from hexadecimal and fail on invalid input.
-    unhex :: Monad m => t -> m t
-
+    unhex :: t -> Either String t
+    -- | Convert from hexadecimal and fail on invalud input.
+    unhexM :: MonadFail m => t -> m t
+    unhexM = either fail return . unhex
 
 instance Hex String where
     hex = Prelude.concatMap w
@@ -34,10 +37,10 @@
     unhex (a:b:r) = do x <- c a
                        y <- c b
                        liftM (toEnum ((x * 16) + y) :) $ unhex r
-    unhex [_]      = fail "Non-even length"
+    unhex [_]      = Left "Non-even length"
 
 
-c :: Monad m => Char -> m Int
+c :: Char -> Either String Int
 c '0' = return 0
 c '1' = return 1
 c '2' = return 2
@@ -60,7 +63,7 @@
 c 'd' = return 13
 c 'e' = return 14
 c 'f' = return 15
-c _   = fail "Invalid hex digit!"
+c _   = Left "Invalid hex digit!"
 
 instance Hex B.ByteString where
     hex = B.pack . hex . B.unpack
diff --git a/hex.cabal b/hex.cabal
--- a/hex.cabal
+++ b/hex.cabal
@@ -1,15 +1,22 @@
+Cabal-Version:       >= 1.10
+
 Name:                hex
-Version:             0.1.2
+Version:             0.2.0
 Synopsis:            Convert strings into hexadecimal and back.
-Description:         Convert strings into hexadecimal and back.
+Description:         Convert strings and bytestrings into hexadecimal and back.
 License:             BSD3
 License-file:        COPYING
 Copyright:           Taru Karttunen <taruti@taruti.net>
 Author:              Taru Karttunen
 Category:            Data
 Maintainer:          taruti@taruti.net
-Build-Depends:       base >= 3 && < 5, bytestring
-Exposed-modules:     Data.Hex
-Extensions:          TypeSynonymInstances FlexibleInstances
-GHC-Options:         -Wall
 Build-Type:	     Simple
+Homepage:            https://github.com/taruti/haskell-hex
+
+library
+  Build-Depends:       base >= 4.10 && < 5, bytestring
+  Exposed-modules:     Data.Hex
+  Default-Extensions:  TypeSynonymInstances
+  GHC-Options:         -Wall
+  Default-Language:    Haskell2010
+