Secure modular design is a method to prevent failures in complex configurable product. After introducing the theory behind the method this paper describes a case study in implementing this method in a real mechanical engineering environment. Much attention has been paid to involving engineers and management in setting up the implementation process, especially in translating the abstract mathematical concepts in the theory to concrete mechanical concepts. Although the method requires serious additional effort in recording design constraints, the participants in the case study expressed confidence in the value of the method.