A basic idea of Model Driven Development (MDD) is to capture all important design information in a set of formal or semi formal models that are automatically kept consistent by tools. This paper reports on industrial experience from use of MDD and shows that the approach needs improvements regarding the architecture since there are no suggested ways to formalize design rules which are an important part of the architecture. Instead, one has to rely on time consuming and error prone manual interpretations, reviews and reworkings to keep the system consistent with the architecture. To reap the full benefits of MDD it is therefore important to find ways of formalizing design rules to make it possible to allow automatic enforcement of the architecture on the system model.