UnboxedSums causes parse error on hash operator e.g. `let (#) = (+)`

GHCi, version 8.1.20160920: http://www.haskell.org/ghc/  :? for help
Prelude> let (#) = (+)
Prelude> :set -XUnboxedSums 
Prelude> let (#) = (+)

<interactive>:3:7: error: parse error on input ‘)’

I first noticed this in an import statement:

import Data.Functor.Utils (Max(..), Min(..), (#.))

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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