The invention concerns a system for supplying hydraulic fluid to a hydraulic system, with an operating reservoir that accepts the hydraulic fluid provided for the operation of the hydraulic system and an auxiliary reservoir connected to the operating reservoir over a hydraulic line for intermediate storage of hydraulic fluid withdrawn from the operating reservoir. According to the invention, an air pump is available that is connected on the one hand on its low pressure side to a suction line that ends in a fluid free area of the auxiliary reservoir, so that a negative pressure can be built up in the auxiliary reservoir as against the external atmospheric pressure, and that is connected, on the other hand, to a control line that is provided with a control opening that is covered by the hydraulic fluid in the operating reservoir at least before the air pump is put into operation.