An improved method of cycle slip prevention in a frequency synthesizer is achieved by determining phase error between a divided VCO and reference, determining whether a phase error of a full cycle slip has occurred and in which direction and altering the phase of the VCO divided signal in the amount and direction to reduce the phase error to less than one reference cycle. The result is an improved transfer function of the PFD, proportional to the phase error in the region −2*pi to 2*pi, and fixed close to maximum when the phase error exceeds the above interval. This invention is achieved with the addition of digital circuitry to monitor and control the PFD and the VCO divider, and does not require additional analog charge pump circuitry.