Abstract. Advanced techniques in separation of concerns such as Aspect-Oriented Programming, help to develop more maintainable and more efficient applications by providing means for modularizing crosscutting concerns. However, conflicts may appear when several concerns need to be composed for the same application, especially when dealing with around advice. We call this problem the Aspect Composition Issue (ACI). Based on our experience in programming aspects, this paper presents a language called CompAr, which allows the programmer to abstractly define an execution domain, the advice codes, and their execution constraints. The CompAr compiler then evaluates the definitions in order to check if the execution constraints are fulfilled. Using a concrete AOP case study, we show how to use the CompAr language in order to detect and avoid ACIs.