GeneralizedNewtypeDeriving doesn't work with data families

Observe:

{-# LANGUAGE TypeFamilies, GeneralizedNewtypeDeriving #-}
module Bug9 where

class C a where
    data D a

instance C Bool where
    newtype D Bool = DInt Int deriving (Eq, Show, Num)

The deriving of Num fails, whereas the corresponding standalone newtype works fine.

Trac metadata

Trac field	Value
Version	6.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	lennart@augustsson.net
Operating system
Architecture