This paper presents a nonlinear modification of the standard linear adaptive optics controller that greatly reduces the startup lag due to saturation in pyramid wavefront sensors (or any wavefront sensor with 4-cell subapertures). Whenever the pyramid sensor is saturated (as determined by an internal model of the saturation in the controller), the deformable mirror signal is adjusted to quickly remove the saturation of the sensor. When the pyramid sensor is not saturated, a standard linear adaptive optics controller is used to generate the deformable mirror signal. The nonlinear controller is compared with a standard linear controller using a CAOS simulation. It is shown that the startup lag is significantly reduced, and that the steady-state performance is identical to the linear controller.