This article focuses on the application of autonomous weapons (AWs) in defensive systems and, consequently, assesses the conditions of the legality of employing such weapons from the perspective of the right to self-defence. How far may humans exert control over AWs? Are there any legal constraints in using AWs for the purpose of self-defence? How does their use fit into the traditional criteria of self-defence? The article claims that there are no legal grounds to exclude AWs in advance from being employed to exercise the right to self-defence. In general, the legality of their use depends on how they were pre-programmed by humans and whether they were activated under proper circumstances. The article is divided into three parts. The first discusses how human control over AWs affects the legality of their use. Secondly, the article analyses the criteria of necessity and proportionality during the exercise of the right to self-defence in the context of the employment of AWs. Finally, the use of AWs for anticipatory, pre-emptive or preventive self-defence is investigated.