The custom often acts as a powerful hindrance to equity-increasing changes. In this paper, we present a simple model of legal dualism in which a progressive legal reform can, under certain conditions, shift the conflicting custom in the direction intended by the legislator. Formal law then acts as an outside anchor that exerts a 'magnet effect’ on the custom. We also characterize the conditions under which a moderate reform performs better than a radical one in improving the welfare of the disadvantaged sections of the population. We illustrate our insights using examples on inheritance, marriage, and divorce in Sub-Saharan Africa and India.