Unable to parse strict annotations when used in a GADT

[iago]

haskell-src-exts is unable to parse the following module

module Bar where

data Foo a where
    Foo :: !a -> Foo a

but it is able to parse this

module Bar where

data Foo a = Foo !a (Foo a)

or this one

module Bar where

data Foo a where
    Foo :: a -> Foo a