A method is disclosed for energy calibrating quantum-counting x-ray detectors in an x-ray installation including at least two x-ray systems turnable around a center of rotation. A target, for producing x-ray fluorescence radiation, is positioned between the first x-ray source and first x-ray detector and irradiated with x-radiation of the first x-ray source in such a way that x-ray fluorescence radiation which strikes the second x-ray detector from the target is produced by the x-radiation of the first x-ray source. The second x-ray detector is then energy calibrated by way of the x-ray fluorescence radiation of the target. The first x-ray detector can be energy calibrated in the same way with the aid of the x-radiation of the second x-ray source. With the proposed method, the x-ray detectors of a dual-source CT x-ray installation can be calibrated with little expenditure under conditions close to those of the system.