The adoption of the Internet technologies favors the diffusion of Web-based applications. However, the development of new applications exploiting the modern interfaces and distribution channels have to face the problems connected with the integration of existing software systems. This aspect often requires the migration of legacy systems toward the Web technologies. They encapsulate a great deal of knowledge and expertise about the application domain and cannot be simply discarded.Many of the migration strategies proposed in the literature assume that the underlying software system is (semi)decomposable where the interface component is separated from the business logic and the data model components. In this case, the interface component can be re-implemented, while the other ones are encapsulated into software wrappers. Unfortunately, legacy systems are very often non-decomposable and alternative solutions are needed. This paper proposes an approach for migrating a non-decomposable software system. The approach consists of redirecting the request of input/output operations to the legacy system by using screen and database proxies. The approach has been applied successfully to Cobol software systems with a character-based user interface.