Kind variables not allowed in data declaration kind annotation

GHC won't accept kind variables stated directly in a data declaration. For example, the following does not compile:

data SMaybe :: (k -> *) -> Maybe k -> * where
  SNothing :: SMaybe s 'Nothing
  SJust :: s a -> SMaybe s ('Just a)

However, the following does compile:

data SMaybe' (s :: k -> *) (m :: Maybe k) where
  SNothing' :: SMaybe' s 'Nothing
  SJust' :: s a -> SMaybe' s ('Just a)

Trac metadata

Trac field	Value
Version	7.5
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture