Determining whether a set of features can be composed, or safe composition, is a hard problem in software product line engineering because the number of feature combinations can be exponential. We argue that synergies between current approaches to safe composition should be exploited and propose a combined approach. At the heart of our proposal is a merge operation that creates a behavioural description for the entire product family from a feature diagram and descriptions of individual feature behaviour. As a result, we intend to verify more efficiently safe composition for an exponential number of feature combinations.