The integration of complex systems out of existing systems is an active area of research and development. There are many practical situations in which the interfaces of the component systems, for example belonging to separate organisations, are changed dynamically and without notification. In this paper we propose an approach to handling such upgrades in a structured and disciplined fashion. All interface changes are viewed as abnormal events and general fault tolerance mechanisms (exception handling, in particular) are applied to dealing with them. The paper outlines general ways of detecting such interface upgrades and recovering after them. An Internet Travel Agency is used as a case study.