$ apt-get update
$ apt-get upgrade
$ apt-get install raspberrypi-kernel-headers
$ echo "deb http://deb.debian.org/debian/ unstable main" | tee --append /etc/apt/sources.list.d/unstable.list
$ apt-get install dirmngr
$ apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 8B48AD6246925553
$ printf 'Package: *
Pin: release a=unstable
Pin-Priority: 150
' | tee --append /etc/apt/preferences.d/limit-unstable
$ apt-get update
$ apt-get install wireguard
$ reboot