  The presence of non-unitary neutrino mixing can affect the measurement of the
three-neutrino leptonic Dirac CP phase and hamper efforts to probe CP violation
due to degeneracies of the extra non-unitary CP phase with the standard CP
phase. We study the effect of including non-unitarity on probing CP violation
with the long-baseline experiments NO$\nu$A, T2K and DUNE. We analyze the
effect of non-unitary mixing at the level of oscillation probabilities
associated with the relevant baselines, and present the CP violation
sensitivity for the individual experiments and their combination. Our results
show that there is an improvement in the CP violation sensitivity of the
combination compared to the individual experiments.
