Regulation by design is an increasingly common approach in the governance of digital technologies. Under this approach, the developers of digital systems must adopt technical measures that implement the specific requirements mandated by law in their software. Some jurisdictions, notably the European Union (EU), have turned to regulation by design as a mechanism to automatically enforce legal requirements, but this article argues that such an approach can have important implications for long-term governance. Drawing from examples of regulation by design in EU law, it shows that by-design provisions delegate rule-making power to software designers, whose interpretations of the law become entrenched in digital systems. This delegation process suffers from legitimacy deficits, which are compounded whenever digital systems continue to enforce the designer-made rules as they operate for years and, sometimes, decades. Yet, these legitimacy deficits are not unavoidable, as regulation by design can be used to force designers to adopt technical and organisational practices that mitigate the risks of rule entrenchment to future generations. By mapping the long-term risks of regulation by design and potential solutions to them, this article provides a first step towards approaches to regulation by design that do not sacrifice the future for present interests.