In democratic societies, international integration requires popular approval. What determines the level of public support for international integration? We argue that national economic performance and the stringency of the proposed integration treaty modify the effects of two individual characteristics on public support: knowledge about the treaty and trust in the incumbent government. Poor economic performance amplifies the positive effect of treaty knowledge because informed citizens value international integration as collective insurance. However, reducing the stringency of the integration treaty through concessions undermines the positive effects of both treaty knowledge and trust in government because concessions mitigate concern even among uninformed and suspicious citizens. To test the theory, we estimate a random utility model on survey data on two repeated referenda on European integration: Maastricht I and II (Denmark, 1992/1993) and Lisbon I and II (Ireland, 2008/2009).