This article shows how the principles of participatory deliberative democracy can serve as a guide for the institutional design of minipublics, while also discussing the obstacles such proposals are likely to face in becoming realised in practice. It does so by discussing the case of citizen-initiated citizens’ assemblies in Flanders, Belgium. This case represents an ambitious proposal that combined elements of petition, deliberation, public consultation and parliamentary deliberation to generate a robust deliberative system. Yet in the end it was soundly defeated in parliament. By studying the institutional specifics of this proposal as well as the macro-deliberative circumstances that led to its failure, this article presents a nuanced picture of the promises and pitfalls of institutionalising deliberative minipublics. It concludes with a call to ‘deliberative activism’.