Collective MPI communications have to be executed in the same order by all processes in their ommunicator and the same number of times, otherwise a deadlock occurs. As soon as the controlflow involving these collective operations becomes more complex, in particular including conditionals on process ranks, ensuring the correction of such code is error-prone. We propose in this paper a static analysis to detect when such situation occurs, combined with a code transformation that prevents from eadlocking. We show on several benchmarks the small impact on performance and the ease of integration of our techniques in the development process.