diff --git a/Data/Encoding/ByteSink.hs b/Data/Encoding/ByteSink.hs
--- a/Data/Encoding/ByteSink.hs
+++ b/Data/Encoding/ByteSink.hs
@@ -101,20 +101,15 @@
     pushWord64be w = PutME $ Right (putWord64be w,())
     pushWord64le w = PutME $ Right (putWord64le w,())
 
-#ifndef MIN_VERSION_mtl(2,0,0,0)
+#if MIN_VERSION_base(4,3,0)
+#else
 instance Monad (Either EncodingException) where
     return x = Right x
     Left err >>= g = Left err
     Right x >>= g = g x
 #endif
 
-instance Throws EncodingException (State (Seq Char)) where
-    throwException = throw
-
-instance ByteSink (State (Seq Char)) where
-    pushWord8 x = modify (|> (chr $ fromIntegral x))
-
-instance ByteSink (StateT (Seq Char) (Either EncodingException)) where
+instance (Monad m,Throws EncodingException m) => ByteSink (StateT (Seq Char) m) where
     pushWord8 x = modify (|> (chr $ fromIntegral x))
 
 newtype StrictSink a = StrictS (Ptr Word8 -> Int -> Int -> IO (a,Ptr Word8,Int,Int))
diff --git a/Data/Encoding/ByteSource.hs b/Data/Encoding/ByteSource.hs
--- a/Data/Encoding/ByteSource.hs
+++ b/Data/Encoding/ByteSource.hs
@@ -103,10 +103,7 @@
     fetchWord64be = getWord64be
     fetchWord64le = getWord64le
 
-instance Throws DecodingException (State [Char]) where
-    throwException = throw
-
-instance ByteSource (State [Char]) where
+instance ByteSource (StateT [Char] Identity) where
     sourceEmpty = gets null
     fetchWord8 = do
       chs <- get
@@ -121,7 +118,8 @@
       put chs
       return res
 
-#ifndef MIN_VERSION_mtl(2,0,0,0)
+#if MIN_VERSION_base(4,3,0)
+#else
 instance Monad (Either DecodingException) where
     return = Right
     (Left err) >>= g = Left err
@@ -143,31 +141,17 @@
       put chs
       return res
 
-instance Throws DecodingException (State BS.ByteString) where
-    throwException = throw
-
-instance ByteSource (State BS.ByteString) where
+instance (Monad m,Throws DecodingException m) => ByteSource (StateT BS.ByteString m) where
     sourceEmpty = gets BS.null
-    fetchWord8 = State (\str -> case BS.uncons str of
+    fetchWord8 = StateT (\str -> case BS.uncons str of
                                   Nothing -> throw UnexpectedEnd
-                                  Just (c,cs) -> (c,cs))
+                                  Just (c,cs) -> return (c,cs))
     fetchAhead act = do
       str <- get
       res <- act
       put str
       return res
 
-instance ByteSource (StateT BS.ByteString (Either DecodingException)) where
-    sourceEmpty = gets BS.null
-    fetchWord8 = StateT (\str -> case BS.uncons str of
-                                  Nothing -> Left UnexpectedEnd
-                                  Just ns -> Right ns)
-    fetchAhead act = do
-      chs <- get
-      res <- act
-      put chs
-      return res
-
 instance ByteSource (StateT LBS.ByteString (Either DecodingException)) where
     sourceEmpty = gets LBS.null
     fetchWord8 = StateT (\str -> case LBS.uncons str of
@@ -194,3 +178,20 @@
       res <- act
       liftIO $ hSetPosn pos
       return res
+    sourcePos = do
+      h <- ask
+      p <- liftIO $ hTell h
+      return $ Just p
+
+{-
+instance Throws DecodingException (State st) => Throws DecodingException (State (Integer,st)) where
+  throwException = throw
+
+instance ByteSource (State st) => ByteSource (State (Integer,st)) where
+  sourceEmpty = sourceEmpty
+  fetchWord8 = do
+    <- fetchWord8
+  fetchAhead = fetchAhead
+  sourcePos = do
+    (p,chs) <- get
+    return (Just p)-}
diff --git a/NEWS b/NEWS
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,8 @@
+Changes from 0.6.4 to 0.6.5
+---------------------------
+
+* Make package work with >=base-4.3.0.0 and mtl-2
+
 Changes from 0.6.3 to 0.6.4
 ---------------------------
 
diff --git a/encoding.cabal b/encoding.cabal
--- a/encoding.cabal
+++ b/encoding.cabal
@@ -1,5 +1,5 @@
 Name:		encoding
-Version:	0.6.4
+Version:	0.6.5
 Author:		Henning Günther
 Maintainer:	h.guenther@tu-bs.de
 License:	BSD3