Questionable behaviours that are perceived as more common also tend to be judged as more morally justified. Here we explore this phenomenon in survey data from 31 countries in the European Values Study, allowing us to examine the universality of the common-is-moral association. More than 35,000 participants rated eight questionable behaviours (e.g., cheating on taxes, having casual sex) on how frequent they are and how justified they are. We estimated common-is-moral associations both across individuals for each behaviour and across behaviours within each individual; in both cases, the association tended to be positive. We further examined the hypothesis that the common-is-moral association would be stronger among less religious people, who are less likely to adopt their moral judgements from religious authorities and therefore should be more susceptible to the heuristic of using the perceived commonness of a behaviour as a guide to how it should be morally judged. Indeed, we found the common-is-moral association to be somewhat stronger among less religious people, whether the association was estimated across individuals or within individuals. We discuss alternative explanations, implications and directions for future research.