Precision laser frequency control is a key requirement for experiments in AMO Physics. At infrared wavelengths, single-sideband modulators offer a frequency tuning of several GHz. Such electro-optic modulators have a dual-parallel Mach-Zehnder interferometer structure. By tuning the phases of the interferometer arms, the carrier and the one sideband can be suppressed. However, drifts in the control voltages require their stabilization to enhance suppression. Existing stabilization methods rely on the modulation of these bias voltages which result in residual amplitude modulation of the single-sideband. Here, we present a novel stabilization method that is based on dual-frequency modulation. The discriminants for sideband and carrier are generated by an additional low- frequency modulation without affecting the amplitude of the desired sideband.