Disable Alarm if pump is OFF.

I have a problem with the configuration of an alarm on my Indusoft application. I want to activate an alarm if the pressure is low only if the pump is running. I have The following tag
(Pressure, PumpOn)

My script.

IF NOT PumpOn THEN
(Pressure-> AlrDisable) = TRUE
ELSE
(Pressure-> AlrDisable) = FALSE
This script works but the problem is that if the alarm is ON before I disable the alarm, the alarm stay ON

Thanks!