The ability to create high-quality software artifacts that are usable over time is one of the essential requirements of the software business. In such a setting, open source software offers excellent opportunities for sustainability. In particular, safeguarding mechanisms against planned obsolescence by any single actor are built into the definition of open source. The most powerful of these mechanisms is the ability to fork the project. In this paper we argue that the possibility to fork serves as the invisible hand of sustainability that ensures that code remains open and that the code that best serves the community lives on. Furthermore, the mere option to fork provides a mechanism for safeguarding against despotic decisions by the project lead, who is thus guided in their actions to consider the best interest of the community.