How does interaction affect categorization, and how might this vary between native and non-native speakers? When people use shared labels to categorize objects, they categorize more similarly to each other. We investigated whether interaction leads non-native speakers to categorize in the same way as native speakers. In six rounds, L1-English and L2-English/L1-Mandarin speakers individually categorized dishware using labels (BOWL, PLATE), then discussed their categories or an unrelated topic after each round. L2 speakers’ categories shifted following category-relevant interaction with L1 speakers, but their categories did not become more L1-like. Unexpectedly, category-relevant interaction reduced alignment within pairs and within language groups; however, this effect was weaker in the L2 than L1 group. Hence, L2 speakers showed a stronger tendency than L1 speakers to use categories that were similar to other speakers from their language group. This suggests that interaction in an L2 can reinforce L2 speakers' categories in their L1.