1. Introduction – 2. Public undertakings as economic operators in procurement markets – 3. The issue at stake: cross-subsidisation of reserved activities – 4. How to prevent cross-subsidisation: separation of accounts, cost allocation and benchmarking 5. How to detect cross-subsidisation in procurement context: Article 69(4) of Directive 2014/24/EU – 6. Critical assessment of the provision – 6.1. The monopoly of the Commission on the substantive assessment of compatibility of the aid – 6.2. Misused aids cannot be excluded – 6.3. The ratio of the norm fails in case of public undertakings – 7. The enforcement of the mechanism at national level: Italy as a case study.