High-level, long-lived radioactive waste remains hazardous for periods that go well beyond our human conception of time (many thousands of years). Because active safety measures are considered unreliable, unjustifiable and simply impossible over such long time spans, experts worldwide recommend geological disposal as the preferred strategy for long-term radioactive waste management, to a large extent due to its promise of delivering ‘passive safety’. Passive safety refers to the repository being safe ‘by itself’, i.e. unmediated by human actors and actions. Safety is thus approached technically and delineated as an intrinsic property of the disposal system. As such, the notion of ‘passive safety’ entails a system simplification that allows for approaching safety in a more calculable and predictable manner than would be the case for ‘active safety’. In this article, we describe and analyze the ambiguity of this seemingly straightforward approach to safety. Drawing on constructivist insights from safety science and science and technology studies, we propose a more integrated sociotechnical vision that transcends the active versus passive safety division. The notion of ‘oversight’, as it is currently starting to surface in international radioactive waste management discourses, will be used as a sensitizing concept, offering potential to elaborate such an integrated vision.