confusing error message

[Dean Herington]

buzzard(118)% cat Bug5.hs
import Control.Monad.State
data S = S Int
newtype M a = M (StateT S IO a)
  deriving (Monad)

main = return ()
buzzard(119)% ghc -c Bug5.hs

Bug5.hs:3:
    Can't make a derived instance of `Monad M'
    (too hard for cunning newtype deriving)
    When deriving instances for type `M'
buzzard(120)% ghc --version
The Glorious Glasgow Haskell Compilation System, version 5.04.2


The real problem above is that I forgot to enable extensions.  It would
be helpful if the error message indicated that as the problem.