GHC Internal error, unboxed sums

$ ./ghc-stage2 -ignore-dot-ghci --interactive
GHCi, version 8.1.20160930: http://www.haskell.org/ghc/  :? for help
Prelude> :set -XUnboxedSums 
Prelude> :kind (# _ | _ #)

<interactive>:1:4: error:
    • GHC internal error: ‘_’ is not in scope during type checking, but it passed the renamer
      tcl_env of environment: []
    • In the type ‘(# _ | _ #)’

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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GHC Internal error, unboxed sums