diff --git a/Data/Encoding/ByteSink.hs b/Data/Encoding/ByteSink.hs
index 551fa24..09f76ae 100644
--- a/Data/Encoding/ByteSink.hs
+++ b/Data/Encoding/ByteSink.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE FlexibleInstances,FlexibleContexts,MultiParamTypeClasses #-}
+{-# LANGUAGE FlexibleInstances,FlexibleContexts,MultiParamTypeClasses,CPP #-}
 module Data.Encoding.ByteSink where
 
 import Data.Encoding.Exception
@@ -101,10 +101,12 @@ instance ByteSink PutME where
     pushWord64be w = PutME $ Right (putWord64be w,())
     pushWord64le w = PutME $ Right (putWord64le w,())
 
+#ifndef MIN_VERSION_mtl(2,0,0,0)
 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
diff --git a/Data/Encoding/ByteSource.hs b/Data/Encoding/ByteSource.hs
index 2b1bdb5..09d1676 100644
--- a/Data/Encoding/ByteSource.hs
+++ b/Data/Encoding/ByteSource.hs
@@ -1,4 +1,4 @@
-{-# LANGUAGE FlexibleInstances,FlexibleContexts,MultiParamTypeClasses #-}
+{-# LANGUAGE FlexibleInstances,FlexibleContexts,MultiParamTypeClasses,CPP #-}
 module Data.Encoding.ByteSource where
 
 import Data.Encoding.Exception
@@ -121,10 +121,12 @@ instance ByteSource (State [Char]) where
       put chs
       return res
 
+#ifndef MIN_VERSION_mtl(2,0,0,0)
 instance Monad (Either DecodingException) where
     return = Right
     (Left err) >>= g = Left err
     (Right x) >>= g = g x
+#endif
 
 instance ByteSource (StateT [Char] (Either DecodingException)) where
     sourceEmpty = gets null