The growing interest in the Service-oriented Architecture paradigm carries along an increasing popularity of choreographies, a flexible form of service composition to manage interactions within a business process. The BPMN provides and intuitive graphical notation to model choreographies, however there are aspects that BPMN choreography diagrams are unable to display, related not to what the participants must do, but to how they should do it. These non-functional requirements are usually expressed using separate, though connected, models. This paper introduces Q4BPMN, an approach that aims at improving the expressiveness of choreography diagrams by enhancing them with non-functional annotations. This way, the participants in the choreography will be eased in knowing what is expected from them, and designers can exploit the underlying formalism to support analysis and monitoring facilities.