<p>The article provides an original analysis aiming at deepening our understanding of solidarity towards illegalised migrants in Europe and its policing. It is based on a single case study. Between 2016 and 2017, up to 13,000 illegalised migrants took refuge in a Catholic church in a working-class neighbourhood of Ventimiglia, Italy, on the border with France. The shelter mobilised more than a hundred volunteers and acted as an important interface with the authorities, NGOs and less structured solidarity. It also provoked hostile mobilisations, operated in a context of increasing criminalisation of aid and under multiple forms of pressure. Based on ethnographic research, including participant observation and taped interviews conducted within the shelter throughout its life, the article focuses on the ways in which it navigated different regimes of legality and degrees of formality, at the intersection of different strands of law. It points to an overlooked effect of policing solidarity, showing how it can lead to organisational transformations and the production of new internal rules. It also shows how individual attitudes towards laws and rules that restrict or discourage assistance are mediated by these organisational assets and norms, as well as by religious socialisation. The article thus goes beyond scholarship on the criminalisation of solidarity and the policing of humanitarianism by pointing to its (less visible) mechanisms and (indirect) effects, and by opening the scope to overlooked social profiles of helpers: faith-based organisations, female parishioners, uneducated and lower-class helpers.</p>