The invention relates to ballast for a discharge lamp (16), comprising a direct-current supply phase (2), semiconductor switches (10, 11), operated at a high-frequency clock frequency for modifying the direction of current through the discharge lamp (16), an ignition transformer (15), which can be supplied with the direct current of the direct-current supply phase (2) via a series capacitor (14) and a choke inductance (17) that is connected to an electrode of the discharge of the discharge lamp (16), said electrode not being connected to the ignition transformer (15). To increase the ignition reliability of the discharge lamp (16), a capacitor (24), connected in series to a switch (23), is connected between a junction point (27) of the series capacitor (14) and ignition transformer (15) on one side and a junction point (26) between the discharge lamp (16) and the choke inductance (17) on the other side, and the capacitor (24) and the choke inductance (17) form a series resonant circuit that is tuned to a higher harmonic of the clock frequency.