The Digital Services Act (DSA) obliges very large online platforms and online search engines to identify, analyse and assess ‘systemic risks’ stemming from the design or functioning of their service and its related systems, including algorithmic systems, or from the use made of their services. This contribution develops the definition of the relevant ‘system’ and applies it to the unlisted risks related to sustainability, thus answering the questions: What system does the term ‘systemic risk’ refer to? When is an unlisted risk a systemic risk? Are risks in the context of sustainability systemic risks within that meaning?