In its recent Green Deal, the Commission reconfirms the importance of public procurement law as an instrument to realise sustainability goals. Public procurement regulation has indeed opened up to more ‘noble’ considerations beyond its traditional principles of non‑discrimination, transparency, and equal competition. From welcoming more socially and environmentally driven award criteria, over an extension of the notion of ‘most economically advantageous’, to the final step of including life cycle costing, sustainability considerations claim an ever more central place. While much ink has been spilled on these issues as such, a reflection on the overall methodology of public procurement law is often absent. Interestingly, ever since Cassis de Dijon, internal market law has experienced a similar evolution through the incorporation of the ‘rule of reason’. This article argues that the same balancing act has become available to contracting authorities, but raises questions as to its appropriateness.