This paper studies how organizational subcultures influence the effectiveness of the enterprise architecture (EA) function. It provides findings from a case study in a European airport company. We find specific subcultural differences that can lower EA effectiveness. In addition, we discover that not only subcultural differences but also subcultural similarity can reduce EA effectiveness. For instance, the preference for working isolated of some business departments results in a lack of communication between those departments, which lowers EA effectiveness. Also, our data suggest that the subcultural influence is indirect. We identify, amongst others, communication defects as an important intermediary variable.