A connection between the disorder in the critical currents of two-dimensional arrays of Josephson junctions and the amount of phase-locking of a row to an external microwave signal is proposed. We have computed the probability of phase-locking as a function of the spread of the critical currents of the individual junctions. The analytic results are in good agreement with numerical simulations. The predictions can be also qualitatively compared to the experiments.PACS. 85.25. Am, 85.25.Cp, 85.25.Na