It seems that the check of a real monitor was introduced by the commit https://gitlab.xfce.org/apps/xfce4-screensaver/-/commit/c44e54350c786497b3bf3835e079d39c39a4951e And it's basically for multi-monitor setups and plug/unplug. Maybe we can assume that the primary monitor is OK even if no monitor info is given? A test fix patch is like below.