{-# LANGUAGE GADTs, DataKinds, PolyKinds, ExplicitForAll #-} module BadTelescope2 where import Data.Kind data SameKind :: k -> k -> * -- This declaration made GHC 8.10 produce a Core Lint error data T a b where MkT :: forall a kx (b :: kx). SameKind a b -> T a b