Technique for calibration of a frequency converter for reducing a leakage-based non-direct-current component at an output of the frequency converter. In an apparatus comprising a frequency converter arranged to perform frequency conversion on an input signal, a local oscillator signal generator arranged to generate an amplitude-modulated local oscillator signal of the frequency converter, and a detector arranged to detect a non-direct-current component of an output signal of the frequency converter, which results from the amplitude-modulated local oscillator signal, an amplitude modulation of an original local oscillator signal by the local oscillator signal generator is controlled, a magnitude of local oscillator leakage of the frequency converter is observed on the basis of the non-direct-current component detected by the detector, and at least one parameter influencing the non-direct-current component of the output signal of the frequency converter is adjusted such that the observed magnitude of local oscillator leakage is reduced.