The coordination of specialist with mainstream service systems is prone to role delineation and implementation difficulties worldwide. In the case of the National Disability Insurance Scheme (NDIS), this specialist/mainstream interface is complicated by federalism and funding responsibilities held by different levels of government. People with disability, especially cognitive or intellectual disability, are over-represented in Australia's prisons. Through semi-structured interviews with professionals working at the interface of disability and criminal justice, we explore some of these interface issues with regard to NDIS services (specialist) in prisons (mainstream). We find that policy permits some NDIS-funded services to be delivered inside prisons, such as transition services related to a person's disability, but in practice there is significant variation in how policy is understood and implemented, leading to exclusion and service gaps. This case study shines light on longstanding debates about service coordination across organisational and jurisdictional boundaries.