Executable models play a key role in many development methods by facilitating the immediate simulation/implementation of the software system under development. This is possible because executable models include a fine-grained specification of the system behaviour. Unfortunately, a quick and easy way to check the correctness of behavioural specifications is still missing, which compromises their quality (and in turn the quality of the system generated from them). In this paper, a lightweight verification method to assess the strong executability of fine-grained behavioural specifications (i.e. operations) at design-time is provided. This method suffices to check that the execution of the operations is consistent with the integrity constraints defined in the structural model and returns a meaningful feedback that helps correcting them otherwise.