A limit switch assembly, for a rising-stem valve having a stem with a diameter and a groove marking a desired stem position, includes an actuator arm having an inner end and an outer end. The inner end of the actuator arm forms a follower. A radius washer is mounted to the outer end of the actuator arm. An electrical switch has an operating lever and is mounted adjacent to the outer end of the actuating arm such that when the actuator arm is in an outward position the radius washer moves the operating lever, operating the electrical switch. When the actuator arm is in an inward position the radius washer does not move the operating lever and the electrical switch is not operated. A bias spring biases the actuating arm toward the inward position.