‘Fattism’ has been described as the last acceptable prejudice. Discrimination on the grounds of weight is experienced regularly by women and men in relation to employment as well as access to goods and services. As I show in this article, it can also be seen as a form of intersectional discrimination. Yet a legal remedy for weight discrimination exists in just a few countries. In this essay, I consider why legal protection is so limited: I highlight the influence of the logic of immutability and suggest that an alternative logic – an anti-stigma principle – should be used to guide the evolution of anti-weight discrimination law.