Oops, forgot to update Arch linux for a while and was met by the following message after trying to run pacman -Syu:

error: failed to prepare transaction (could not satisfy dependencies)
:: package-query: requires pacman<4.3

This is because there was a change in the library that bridged between yaourt and pacman.

To fix, remove package-query and manually install the snapshot from AUR:

pacman -Rdd package-query
git clone https://aur.archlinux.org/package-query.git
cd package-query
makepkg -si

You should now be clear to run pacman -Syu.