ScopedTypeVariables & PolyKinds lead to weird error message

When I try to compile

{-# LANGUAGE ScopedTypeVariables, RankNTypes, PolyKinds #-}

module Bug where

import Data.Proxy

foo = (undefined :: Proxy a) :: forall a. Proxy a

I get

Bug.hs:7:27:
    Kind variable ‘k’ used as a type
    In an expression type signature: Proxy a
    In the expression: (undefined :: Proxy a) :: forall a. Proxy a
    In an equation for ‘foo’:
        foo = (undefined :: Proxy a) :: forall a. Proxy a

This is all the more odd given that k does not appear in my code!

This bug happens both in HEAD and in 7.8.1 RC 2.

Trac metadata

Trac field	Value
Version	7.8.1-rc2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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