We have developed and evaluated a method to correct for detector cell response variations in photon-counting X-ray detectors with energy discrimination capability. With these detectors, variations in energy thresholds or energy response of the detector cells can result in spectral-dependent nonuniformities in sinograms that produce rings in reconstructed images. The proposed method is basis material decompositionbased and corrects variations in the spectral sensitivity of detector cells to reflect the characteristics of a standard detector cell. requires calibration similar to that used in basis material decomposition methods and does not require knowledge of the exact energy spectrum, energy thresholds, or energy response of the individual detector cells. Both simulation and physical experiments studies showed substantial reduction in nonuniformity in sinograms and of rings in reconstructed images.