Unboxed record hard error

[Lucas Escot]

The following code produces a hard error (seemingly thrown by Agda, but most likely comes from agda2hs):

open import Haskell.Prelude

record BinInt : Set where
  field
    int : Integer
{-# COMPILE AGDA2HS BinInt unboxed #-}

An internal error has occurred. Please report this as a bug.
Location of the error: __IMPOSSIBLE__, called at src/full/Agda/TypeChecking/Monad/Base.hs:2964:18 in Agda-2.6.4.1-d94eea85a1ca96c3755bdb85f3292bdd72fd5471203eca704b0e7066d091a850:Agda.TypeChecking.Monad.Base

If I remove the unboxed, no error. But I need the unboxed!