The article examines the conceptual and normative “riddle” posed by art. 6 of the EU Artificial Intelligence Act (AIA) in defining “high-risk” AI systems (h-AISs). It argues that the combination of a horizontal, technology-neutral framework with a risk-based classification generates significant interpretative uncertainty and undermines legal certainty. After situating the AIA within the broader EU product-safety regime and the New Legislative Framework, the contribution meticulously examines in detail the critical issues arising under Art. 6 AIA. These range from para. 2 recalling the Annex III list of high-risk AI systems, which does not rest on an objective assessment of risk, to the exceptions in paras. 3 and 4, and the cross-reference to Union harmonisation legislation in Annex I. Particular attention is paid to contested notions such as “safety component” and “third-party conformity assessment required”, illustrated through case studies (e.g. security mobile robots, humanoid robots, drone docking stations). The article concludes that this unstable definitional architecture undermines consistent application, equal treatment across sectors, and effective incentives for innovation.