In this paper we deal with compensation for controller windup due to actuator saturation in the integral sliding mode control. It is shown that the actuator saturation in the integral sliding mode control causes windup problem similar to the so-called integrator windup, which often takes place in linear control systems with integral action. A simple modification for the switching function is presented in order to reduce the discontinuous component of the control input during saturation. This can be seen as a variable switching function. Furthermore, the proposed anti-windup compensation is applied to a power-assisted manipulator with a single degree of freedom. Simulation and experimental results show the effectiveness of the proposed method.