Electric energy meters have always been designed to account energy under sinusoidal conditions, and therefore, the uncertainty specification outside these conditions was of little interest. This was considered acceptable when the voltage and current distortion level was low and the old well-known induction meters were used. In fact, under these conditions, the measurement errors caused by distortion did not generally penalize the customers. The present situation is, however, quite different: Distortion is not any longer negligible, particularly in low-voltage systems, and the modern electronic energy meters can be much more sensitive to distortion than the induction meters, depending on the implemented measurement algorithm. This paper briefly discusses the calibration problems raised by the electronic energy meters and proposes a new calibration procedure, fully compliant with the recent Directive of the European Parliament on the measuring instruments, and based on a synthesizer of randomly distorted signals.