Watching others receive superior treatment, a phenomenon known as the bystander effect, typically results in negative customer responses. In contrast, we investigate how to encourage positive responses from bystanders. The results of our experimental and survey studies show that witnessing preferential treatment leads bystanders to experience envy, which then triggers self-enhancement motivation that influences future intentions about participating in a loyalty program. In addition, when bystanders know the rules that allow preferential treatment, self-enhancement motivation encourages them to participate in the loyalty program. Theoretical contributions and practical implications for managing loyalty rewards programs are discussed.