GHC crashes on synonym family in a rank-n type

{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE RankNTypes #-}

module Boom where

type family F a :: *

data Boom = Boom (forall a. F a)
  deriving Show

When loading the above compilation unit into GHCi, it crashes with:

ghc: panic! (the 'impossible' happened)
  (GHC version 6.10.1 for i386-apple-darwin):
	TcTyFuns.flattenType: synonym family in a rank-n type

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
Operating system
Architecture