A method and a device for detecting a fiber lap on a rotating machine component, wherein a sensor signal is used to detect the fiber lap that has formed on the circumference of the component. To enable a noncontacting monitoring despite unfavorable environmental conditions, the sensor signal includes ultrasound, and an echo sound signal is evaluated to detect the presence of a fiber lap. In one disclosed embodiment, the detecting device is used in association with a fiber cutting machine for cutting tow, and which includes a rotating cutting blade holder and a rotatable pressure ring, which cooperate for cutting the tow. To achieve a shutdown of the machine as quickly as possible upon formation of a fiber lap, the fiber lap is directly monitored on the circumference of the pressure ring by means of a sensor unit which has an ultrasonic transmitter and a sound receiver.