Street-level bureaucrats implementing nation states’ migration policies increasingly find themselves in a structural tension between providing social assistance and regulating the flows of people entering and leaving the national territory. As a result, doing migration work involves a wide range of difficult, ambivalent situations. This article examines how and under which conditions these tensions translate into moral and political dilemmas in street-level bureaucrats’ everyday work. In doing so, it draws upon original qualitative research with street-level bureaucrats working in the Belgian programme for assisted voluntary return. The article concludes by proposing an approach centred around the notion of immunisation so as to understand the social context in which ambivalence and its contraries are produced.