I solved this by:
mv /etc/init.d/asterisk ~/asterisk.init.d.bak
vi /etc/systemd/system/asterisk.service
… and I put in …
[Unit]
Description=Asterisk PBX and telephony daemon
Documentation=man:asterisk(8)
Wants=network.target
After=network.target
[Service]
Type=simple
User=asterisk
Group=asterisk
Environment=HOME=/var/lib/asterisk
WorkingDirectory=/var/lib/asterisk
ExecStart=/usr/sbin/asterisk -f -C /etc/asterisk/asterisk.conf
ExecStop=/usr/sbin/asterisk -rx 'core stop now'
ExecReload=/usr/bin/asterisk -rx 'core reload'
# safe_asterisk emulation
Restart=always
RestartSec=10
[Install]
WantedBy=multi-user.target
… and then running …
systemctl deamon-reload
systemctl enable asterisk
systemctl restart asterisk
Hope this helps someone.
With minor modifications, the service comes from here: