Fractional-N frequency synthesizers can exhibit a phenomenon known as wandering spurs. This brief traces the root cause of the phenomenon to the divider controller. Predictions of the repeat period and the wander rate in the case of a multi-stage noise shaping delta-sigma modulator (MASH DDSM)-based divider controller are given. Simulations, based on CppSim simulations of a type-II CP-PLL with a third-order digital delta-sigma based divider controller, confirm the theoretical predictions.