The dependency [alchemy/zippy: "^0.3"](https://packagist.org/packages/alchemy/zippy#0.4.8) includes `doctrine/collections: "~1.0"` which slides up to current [doctrine/collections version 1.5](https://packagist.org/packages/doctrine/collections#v1.5.0) which has a hard requirement for PHP 7.1. As far as I can tell, alchemy/zippy works great for doctrine/collections <1.5. So, two options going forward: 1. This project just has a hard dependency on PHP 7.1, no support for PHP 5.6 1. We do some composer ju-ju to force this "grandchild" dependency of doctrine/collections to <1.5.