The paper addresses the issue of possible responsibility of a member state for acts of an international organization of which it is a member. This particular issue forms part of the on-going work of the International Law Commission of establishing rules for the responsibility of international organizations. The particular challenge is posed by possible “responsibility gaps”, i.e. situations where a state might avoid compliance with its own obligations by prompting the organization of which it is a member to act instead. The paper compares the ILC approach, approaching the issue by way of trying to establish general rules of responsibility (“secondary rules”) and the practice of the EU, which has addressed the issue by tailor-made solutions in the context of specific treaties (“primary rules”). The latter approach is more flexible as it allows individual solutions pertinent to particular circumstances and treaty regimes so as to ensure that either the organization itself or its member state is responsible, depending whichever is genuinely responsible. The paper concludes that the ILC work is progressing in the right direction as it narrows down the possibilities where a member state can be held responsible to cover only situations bordering abuse, rather than more open-ended standards for individual member state responsibility, which can open the door for unpredictable results.