How to use HHVM with systemd / journald / syslog?

I'm experimenting with hhvm on Debian 7 (Wheezy). I have systemd 215 installed and am using this unit file to run hhvm:

``` ini
[Unit]
Description=hhvm
After=network.target

[Service]
Type=oneshot
ExecStart=/etc/init.d/hhvm start
ExecStop=/etc/init.d/hhvm stop
RemainAfterExit=true

[Install]
WantedBy=multi-user.target
```

But I can't figure out how to get it to work with journald (i.e. I don't want it to log to a file).

I tried messing with these variables in `/etc/hhvm/server.ini` but nothing helped:
- `hhvm.log.use_syslog`
- `hvm.log.file`
- `hhvm.log.use_log_file`

I'd always get this error when running `systemctl start hhvm.service`:

> **Log file not specified under daemon mode.**