Prospects for democracy in multi-ethnic societies are generally more promising if elections are not mere ethnic censuses, in which people vote predominantly for co-ethnic parties and candidates. But what institutions facilitate or hinder ethnic voting? Unlike past studies, this article explores ethnic voting by conducting a natural experiment (rather than surveys or laboratory experiments). It examines the case of Fribourg, a bilingual (French/German) Swiss canton where elections at different levels of government, within the same electoral district, are held under both majoritarian and proportional systems. Coupled with the high territorial homogeneity of the linguistic groups, this unique setting allows us to conduct a robust empirical analysis of voter behaviour. We find that cross-ethnic voting is significantly more frequent in multi-member majoritarian elections than in list-PR elections or in two-member majoritarian elections. Our results yield qualified support to the centripetalist approach to electoral design in multi-ethnic societies, that favours majoritarian systems, rather than to the consociational school that advocates proportional representation.