When like-minded people discuss with each other, i.e. engage in ‘enclave deliberation’, their opinions tend to become more extreme. This is called group polarization. A population-based experiment with a pre-test post-test design was conducted to analyze whether the norms and procedures of deliberation interfere with the mechanisms of group polarization. Based on a survey, people with either permissive or restrictive attitudes toward immigration were first identified and then invited to the experiment. The participants were randomly assigned to like-minded and mixed small-n groups. Each like-minded group consisted of only permissive or restrictive participants, whereas each mixed group consisted of four permissive and four restrictive participants. The like-minded treatment represents enclave deliberation, and the mixed treatment a ‘standard’ deliberative mini-public design. The main finding of our experiment is that people with anti-immigrant attitudes become more tolerant even when they deliberate in like-minded groups. Moreover, similar learning curves are observed in both treatments. Based on the results, we conclude that deliberative norms can alleviate the negative consequences of discussion in like-minded groups.