A number of detailed safety functions for a granitic host rock, subordinate to the main functions containment and retardation, are presented, based on SKB’s safety assessment SR-Can for the KBS-3 concept. The host rock should provide a favourable environment for the repository from the point of view of chemical, hydraulic and radionuclide transport, mechanical and thermal properties, which are further specified as a number of subordinate safety functions. These are strongly linked to the functions and properties of the canister and the clay buffer in the KBS-3 concept. Issues related to geosphere stability during the one million year assessment period are discussed and primarily relate to perturbations caused by future colder and dryer climates yielding glacial and/or permafrost conditions and the impact these perturbations may have on the safety functions. In the SR-Can assessment, it was concluded that the granitic host rocks at the analysed sites provide a sufficiently favourable and stable environment for the vast majority of the 6 000 analysed deposition holes. The residual radiological risks associated with the repository, as pessimistically calculated based on preliminary understanding of the two candidate sites, are, from the point of view of the host rock, sensitive to details in the repository layout. In particular, it is important to be able to avoid deposition holes intersected by large or highly transmissive and hydraulically connected fractures and thus to understand and being able to quantify the heterogeneous character of the fractured host rock, in particular at repository depth. A number of issues related to geosphere stability where improved knowledge could lead to more realistic assessments are also identified.