Recent research has indicated that social heterogeneity impacts party system size, even in restrictive settings. This research as yet has not established whether it is minority or majority voters who are behaving outside Duvergerian expectations. This study argues that it is ethnic voters that seem to defect from their parties at lower rates, which explains why small parties proliferate and persist in heterogeneous states. This hypothesis is tested on party-in-district level election returns in the German lander Schleswig-Holstein. The results show that small ethnic parties suffer notably less defection than small non-ethnic parties. The study proposes a number of potential causal mechanisms that could be driving ethnic voters, as a group, to defect at lower rates than non-ethnic voters.