In this article we discuss how to improve the resilience of an existing control system. In recent years, our environment has become populated with numerous control systems due the to availability of low-cost technologies. For instance, modern home automation has become a cooperative network of multiple control systems, many of which communicate over the Internet. Many of these systems hardly address resilience, and improving them is hard, as many of them are provided as “black boxes”. Consequently, as the main contribution, we propose a method for introducing resilience to an existing control system. The method is based on designing and adding resilience mediators that act in between the components to correct faulty communication and to mediate state awareness. In the method, behavioral analysis and HAZOP tables are used as tools to identify and design the relevant resilience mediators. We illustrate the use of the proposed method with an ongoing, real-life case study involving the control of a residential building that adapts to occupant’s behavior.