We have studied numerically the decay of the self-dynamic structure factor (SDSF) for a small particle diffusing in a colloidal glass. We show that, in line with theoretical predictions, the super-Burnett coefficient (characterizing the deviation of the fourth moment of the single particle distribution from its Gaussian value) is finite. However, our results also show that large scale deviations from Fick's law of diffusion should still be easy to detect experimentally. These deviations take the form of the SDSF decaying algebraically rather than exponentially as Fick's law would predict.