Interactions between Web services are based on interfaces which describe Web services on both structural and behavioural perspectives. It can happen that the interface provided by a service does no longer match (for instance, because of an evolution) the interface required by its partners. In this situation, and until the required interfaces are fixed, interactions cannot succeed. To address this issue, and focusing on the behavioural part of interfaces, we propose an approach based on a mediator, automatically generated, which aims to seamlessly resolve incompatibilities during service interactions.