Suspend button does not work when xscreensaver is active on xfce Debian

I've Debian jessie and xfce. When I push the power button, my system is suspended. When I press any key on my keyboard the system wake up and I get the login prompt of Xscreensaver (screen lock is active). Now if I push the power button the system does not suspend, I must login and then I can suspend the system with the power button. Is there a way to suspend the system from the login screen of Xscreensaver?