polykinds error: Found `k' but expected `k'

{-# OPTIONS -XTypeFamilies -XDataKinds -XPolyKinds #-}

class Foo (xs :: [k]) where 
    type Bar xs :: *
    
instance Foo '[] where
    type Bar '[] = Int

fails with:

I:\a.hs:7:5:
    Type indexes must match class instance head
    Found `k' but expected `k'
    In the type instance declaration for `Bar'
    In the instance declaration for `Foo '[]'

If I change the kind of xs from [k] to [*], the program is accepted.

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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