We argue that female Diana monkeys ( Cercopithecus diana ) can form complex calls by combining an A call with other elementary calls. We reject (on both empirical and conceptual grounds) a combination-free analysis based on accidental homophony, and we consider two main analyses: the Acoustic Theory takes the combination to be merely acoustic, whereas the Affixal Theory takes A to function as a suffix. We provide limited arguments for the Affixal Theory, and through comparison with another closely related monkey species, we date these combinations to at least 6 million years ago.