Systemd backed tmpfs | How to specify /tmp size manually

I mount /tmp on tmpfs using: sudo systemctl enable tmp.mount sudo systemctl start tmp.mount But this way /tmp takes up all the free RAM: $ df -h /tmp Filesystem Size Used Avail Use% Mounted on tmpfs 3.9G 12K 3.9G 1% /tmp $ **How do I tell systemd tmp.mount to use only 1G?** I know I can alternatively not use systemd and manually add an entry to /etc/fstab and specify the size there. But I don't want to do that. I want to use systemd backed tmpfs.