diff --git a/man/systemd.timer.xml b/man/systemd.timer.xml
index eb0afee141..0d0cccf152 100644
--- a/man/systemd.timer.xml
+++ b/man/systemd.timer.xml
@@ -73,6 +73,12 @@
foo.timer activates a matching service
foo.service. The unit to activate may be
controlled by Unit= (see below).
+
+ Note that in case the unit to activate is already active at the time the timer elapses it is not restarted,
+ but simply left running. There is no concept of spawning new service instances in this case. Due to this, services
+ with RemainAfterExit= set (which stay around continously even after the service's main process
+ exited) are usually not suitable for activation via repetitive timers, as they will only be activated once, and
+ then stay around forever.