Packaging: where should I install the systemd configuration?

Hi! I’m working on a private Trisquel package for my program. My program installs a systemd service file, and a timer. I tried to install them in $sysconfdir/systemd/system, but then lintian complains that they should go in /usr/lib/systemd/system instead. Fine, I put them in $libdir/systemd/system. However, they end up installed in ./usr/lib/x86_64-linux-gnu/systemd/system/ and systemd can’t find them! What can I do to have them installed in /usr/lib/systemd/system?