For sure, this was pretty much a copy-paste job. At first I thought that I should try and use a multi-buildpack and then have yesod dependencies separately: E.g. https://github.com/rehno-lindeque/heroku-buildpack-yesod-dependencies (which was partly ripped off from another buildpack that seems to be intended for generically including vendor binaries). I couldn't get this to work unfortunately, I'm still not sure if that could perhaps be a better approach.