A reliable method of aligning a printing plate against a stop includes moving the printing plate and the stop relative to each other, detecting temperature changes occurring at a temperature sensor connected to the stop, when the printing plate comes into contact with the stop, deriving signals indicating the position of the printing plate relative to the stop from the signals of the temperature sensor, and deriving a signal indicating the thermal conductivity between the printing plate and the stop from a speed of change of the temperature sensor signal. A signal indicating incorrect alignment of the printing plate against the stop is output if the thermal conductivity drops below a predetermined threshold.