The invention relates to a choke for operating a gas discharge lamp, which comprises an inverter (1) that has two transistor switches (17 and 18) that are connected in series to a direct voltage source (Ubus) in a push-pull circuit. The inverter (1) is linked with a load circuit (3) via a coupling capacitor (2) to which a high-impedance resistor (12) is connected in parallel, said load circuit comprising the gas discharge lamp (4) and an acceptor circuit (22). A sensor circuit (6) is used to detect both a lamp malfunction and the voltage applied to the lamp (4). The sensor circuit (6) is provided with a voltage divider (7) that is connected in parallel to the lamp filaments (8, 9) and the resonance capacitor (5) on the side facing away from the coupling capacitor (2) of the lamp (4). A sensor signal (10) detects a lamp malfunction or determines the lamp voltage that is tapped in a center (11) of the voltage divider (7).