This article proposes to focus on vulnerability in the operationalisation of securitisation theory. It argues that in empirical investigations we often fail to acknowledge that security acts may reflect weakness, not strength. Employing second-generation securitisation research, it first problematizes the common approach to securitisation. Namely, that the self-referential conceptualisation of security acts, together with the realist understanding of power, lead to interpretations of securitisation as a tool of unprincipled statecraft. Secondly, drawing on Brown’s work on border walling, the article reasons that securitisation is predicated on vulnerability. Vulnerability is a legitimising necessity of securitisation. One cannot designate a...