This article provides a geographical analysis of the contribution of social housing to income segregation in France from 1999 to 2015 at very detailed spatial scale. During this period, a law required some French municipalities (with more than 3500 inhabitants in large conurbations) to build more social housing to reduce segregation. Surprisingly, it appears that while home tenure (social vs private housing) segregation has been decreasing, income segregation has been rising. With segregation decomposition techniques, we provide evidence that this is a side-e¤ect of the legal framework: decreasing income segregation in the geographical scope of the law but a ‡ight e¤ect of middle and upper class households out of it.