Design errors cause high costs during the development of software, since such errors are often detected quite late in the software development process. Hence, it is desirable to prevent design errors as early as possible, i.e. it is necessary to specify constraints on the software design. While there are a number of approaches available that permit to specify such constraints, a common problem of those is that the developers need to specify constraints in a different language than their design language. However, this reduces the acceptance of such approaches, as developers need a different language just for the purpose of specifying constraints. This paper proposes an approach that permits to specify constraints within the UML by using Join Point Designation Diagrams (JPDDs).