Social norms can mitigate the effectiveness of formal institutions, in particular the way legal reforms may affect women's autonomy. We examine this question in the context of ethnic variation in traditional post-marital cohabitation, i.e. matrilocality versus patrilocality. We use within-country variation in ethnic kinship practices in Indonesia, exploiting a major legal reform that exogenously fostered women's access to justice and their ability to divorce. We theoretically establish that compared to women of patrilocal tradition, matrilocal women should divorce relatively more after the reform and, for those in stable marriages, experience a relative increase in empowerment. We test these predictions using double-difference estimations with fixed effects. We confirm the relative increase in divorce among matrilocal women and, for those who stay married, a relative improvement in a wide range of outcomes for them and their children. We also predict higher benefits for matrilocal women experiencing a larger drop in divorce costs, which we test with triple-difference estimations exploiting the distance to courthouses. Our results encourage tailored policies that may transcend cultural contexts and overcome the adherence to informal laws.