diff -ru orig/src/Data/Bytes/Serial.hs new/src/Data/Bytes/Serial.hs
--- orig/src/Data/Bytes/Serial.hs	2014-02-22 21:21:31.076773095 +0200
+++ new/src/Data/Bytes/Serial.hs	2014-02-22 21:21:29.000000000 +0200
@@ -58,7 +58,9 @@
 import Data.Int
 import Data.Bits
 import Data.Monoid as Monoid
+#if MIN_VERSION_base(4, 6, 0)
 import Data.Ord (Down(..))
+#endif
 import Data.Functor.Identity as Functor
 import Data.Functor.Constant as Functor
 import Data.Functor.Product  as Functor
@@ -475,9 +477,11 @@
   serialize = serialize . (fromIntegral::Int -> Int8) . fromEnum
   deserialize = (toEnum . (fromIntegral::Int8 -> Int)) `liftM` deserialize
 
+#if MIN_VERSION_base(4, 6, 0)
 instance Serial a => Serial (Down a) where
     serialize (Down a) = serialize a
     deserialize = Down `liftM` deserialize
+#endif
 
 instance Serial Version where
     serialize (Version vb ts) = serialize (fmap VarInt vb, ts)