The right of self-defence against non-state actors is increasingly invoked and accepted in the practice of states. However, the recognition of this right must overcome a fundamental obstacle: that of explaining why the rights of the host state, in particular its right of territorial sovereignty, is not infringed by the self-defensive force used within its territory. In practice, states invoking self-defence against non-state actors rely on the involvement of the host state with those actors to justify the use of force in that state's territory. It is not clear, from a legal standpoint, how to rationalize the fact of involvement as a form of legal justification. For some, involvement amounts to attribution. For others, involvement is a form of complicity. For others still, involvement may entail a breach of the host state's due diligence obligation to protect the rights of other states in its territory. All of these solutions are deficient in some way, and have failed to receive general endorsement. This article considers whether there may be a different, as yet neglected, solution: self-defence as a circumstance precluding wrongfulness. The article shows that this is not a perfect solution either, since positive law remains uncertain on this point. Nevertheless, it is a solution that may provide a better normative framework for the development of the law of self-defence against non-state actors.