In today’s society, we can easily connect with people who share our ideas and interests. A problem with this development is that political reasoning in like-minded groups easily becomes lop-sided since there is little reason to critically examine information that everyone seems to agree with. Hence, there is a tendency for groups to become more extreme than the initial inclination of its members. We designed an experiment to test whether introducing deliberative norms in like-minded discussions can alleviate such group polarization. Based on their attitudes toward a linguistic minority, participants were divided into a positive and a negative opinion enclave. Within the two enclaves, the participants were randomly assigned to group discussions either with or without deliberative norms. Both face-to-face and online discussions were arranged. We found that free discussion without rules led to group polarization in like-minded groups, whereas polarization could be avoided in groups with deliberative norms.