Within the broader debate on the extended mind, this paper discusses the usefulness of vehicle externalism for understanding willpower and self-control. People often use external constraints to limit their future action possibilities in order to obtain outcomes that are considered now to be preferable, as opposed to what people would do in the future without such constraints. The episode of Ulysses with the Sirens famously illustrates this strategy, known in the literature on self-control as pre-commitment. The question addressed in this paper is whether or not this use of external constraints to achieve self-control constitutes a legitimate instance of extended decision-making. After reviewing several pre-commitment strategies and clarifying what differentiates willpower from self-control, I argue that the latter can be (and often is) extended, but not the former.