standalone binary deriving

[Ben]

compiling the following fragment in ghci

{-# LANGUAGE StandaloneDeriving #-}

import Data.Binary (Binary)

newtype Pair a b = Pair (a,b)
deriving instance (Binary a, Binary b) => Binary (Pair a b)

results in the following message:

Prelude> :load "/Users/catbee/Documents/dev/haskell/savestream/foo.hs"
[1 of 1] Compiling Main             (
/Users/catbee/Documents/dev/haskell/savestream/foo.hs, interpreted )
ghc: panic! (the 'impossible' happened)
  (GHC version 6.12.1 for i386-apple-darwin):
	genDerivBinds: bad derived class
    binary-0.5.0.2:Data.Binary.Binary{tc rkt}

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

should i file a bug report?

b