[Discovered by crater](https://crater-reports.s3.amazonaws.com/beta-1.31-2/beta-2018-11-13/reg/cage-0.2.6/log.txt), looks like: ``` $ git clone https://github.com/faradayio/cage $ cd cage $ cargo test --no-default-features # passes $ cargo +beta test --no-default-features # ICEs ``` cc @rust-lang/compiler, cc @emk