When do international treaties cause domestic policy adjustments? While previous research emphasizes the consequences of treaty ratification, we argue that the need to secure entry into force can induce states to change their policies already before ratification. If a state expects benefits from a treaty, it can increase the probability of foreign ratification by implementing policies that benefit pivotal domestic players within its partner country. Accordingly, studies that focus on policy change after ratification underestimate the importance of treaties and partly misconstrue the causal connection between treaties and policies. We test the theory against data on the relationship between North–South preferential trading agreements (PTAs) and automobile emission standards, finding that developing countries adopt automobile emission standards between the signature and ratification of North–South PTAs.