Any approach to efficiency calibration of HPGe detectors sensitive to low-energy gamma-rays and X-rays has to deal with true coincidence summing. We developed a method based on the integration of the EFFTRAN code into the commercial Genie2K™ gamma-ray spectrometry software. EFFTRAN's role is to compute true coincidence summing corrections and to obtain satisfactory results for detectors sensitive to X-rays. EFFTRAN had to be upgraded to include a full simulation of the emission of X-rays. In this manner, efficiency calibrations were successfully set up for BeGe and XtRa detectors.