This article uses the case of Denmark to critically discuss key assumptions in the theoretical literature on dual citizenship. When Denmark surprisingly accepted dual citizenship in 2015, the decision reflected two distinct lines of argument: first, accepting dual citizenship would allow Danes living abroad to keep their Danish citizenship; second, because it is considered illegitimate to make people stateless, allowing dual citizenship would simultaneously allow for citizenship revocation of dual citizens who engage in or support acts of terror. This rationale stands in striking contrast to how dual citizenship has been previously theorised. The gradual acceptance of dual citizenship in Western countries since the early 1990s has been seen either as a symptom of a post-national era or as a pragmatic adjustment to the transnational realities of international migration. By contrast, the case of Denmark shows that dual citizenship may serve as a lever to protect the political community of the nation-state from terrorism and, as such, function as a tool of securitisation.