ghc -haddock fails to parse doc comments in closed type families

GHC with -haddock fails to parse the following program:

{-# LANGUAGE TypeFamilies #-}
module Bug where

type family Closed a where
  -- |This comment fails to parse
  Closed Int = Bool

ghc -haddock Bug.hs
[1 of 1] Compiling Bug              ( Bug.hs, Bug.o )

Bug.hs:5:3: parse error on input ‘-- |This comment fails to parse’

(tested with 7.10.3 and an slightly out-of-date HEAD)

Trac metadata

Trac field	Value
Version	7.10.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Parser)
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