When popular referendums fail to ratify new international agreements or succeed in reversing existing ones, it not only affects domestic voters but also creates negative spillovers for the other parties to such agreements. We explore how voters respond to this strategic environment. We use original survey data from a poll fielded just one day before the 2015 Greek bailout referendum—a referendum in which the stakes for other countries were particularly high—to investigate how expectations about the likely foreign response to a noncooperative referendum outcome influence voting behavior and to what extent foreign policymakers can influence those expectations. Our analysis of the Greek referendum shows that such expectations had a powerful effect on voting behavior: voters expecting that a noncooperative referendum outcome would force Greece to leave the eurozone were substantially more likely to vote cooperatively than those believing that it would result in renewed negotiations with the country's creditors. Leveraging the bank closure that took place right before the vote, we also show that costly signals by foreign actors made voters more pessimistic about the consequences of a noncooperative vote and substantially increased the share of cooperative votes.