An oil mist separator has a pressure regulator valve which is located in the blow-by line downstream of the oil mist separator element in the flow direction of the gas. The pressure regulator valve has a bias so that it opens above a specified pressure difference between the blow-by line and a neighboring chamber. Located around the oil mist separator element is a bypass line which has a bypass valve. The bypass valve has a bias that causes the bypass valve to close below a specified pressure difference between the suction side and the pressure side of the oil mist separation element. The pressure regulator valve and the bypass valve are connected with each other so that the pressure regulator valve, as it closes, increases the bias of the bypass valve.