Conformity is an important aspect of many communication systems in which signals are culturally transmitted. We suggest that one reason for it to evolve is if nonconforming individuals are discriminated against, and we therefore investigated how this might arise. We designed a spatial simulation, in which individuals occupied a territory on a lattice, and played a territorial game with their neighbours in which one individual could challenge another and, if successful, obtain some of the latter's resources. We then examined the relative success of pairs of strategies. We found that aggression targeted towards nonconformers (conformity-enforcing behaviour) was more successful than randomly targeted aggression in both a simple model and a more complicated one in which the conditions were based on the specific case of song sharing between songbirds. The reason for this result is that individuals could use patterns of vocal sharing to gang up on neighbours with locally uncommon song types, increasing their own chances of success. In both models, a critical parameter was how the number of contests an individual was previously involved in altered the chance of winning: conformity-enforcing behaviour was the most successful strategy only if the more contests an individual had been involved in, the less likely it was to win. Our results may explain the origin of conformity-enforcing behaviour and discrimination in nonhuman animals and may have relevance to similar behaviour in humans.