Specify submodule revision in PKGBUILD

I'm trying to install [hhvm-git](https://aur.archlinux.org/packages/hhvm-git/) package from AUR and getting an error. There is a bug in one of submodules. This bug is fixed already and I want to specify revision contains that fix for the submodule. How can I do that? In PKGBUILD I tried to specify revision as suggested in [Arch Wiki](https://wiki.archlinux.org/index.php/VCS_package_guidelines) (line in source array): "git+https://github.com/facebook/proxygen#7e37f926d922b55c85537057b57188dea9694c32 " Result: -> Creating working copy of proxygen git repo... remote: Counting objects: 6, done. remote: Compressing objects: 100% (6/6), done. remote: Total 6 (delta 4), reused 0 (delta 0) Unpacking objects: 100% (6/6), done. From /tmp/yaourt-tmp-german/aur-hhvm-git/proxygen 7e2a49c..3395064 master -> origin/master ==> ERROR: Unrecognized reference: 7e37f926d922b55c85537057b57188dea9694c32