In a thick matter pump, especially for delivering concrete, comprising two delivery cylinders, it is known to provide two position sensors in one of the two cylinders for control of the pistons. However, leakage of hydraulic fluid can lead to an imbalance of the two cylinders. In the invention two position sensors (52, 52";) are provided, which are arranged at a defined distance from one of the ends of the drive cylinders and which respond to a drive piston (30, 30";) that is passing by. To prevent the formation of concrete clots inside the delivery cylinders (10) and to prevent the occurrence of a slamming when the drive pistons (30, 30";) reach their end of travel, the invention provides that both position sensors (52, 52";) are arranged at a distance from the piston rod-side ends of both drive cylinders (24, 24";) and, in addition, a correcting sensor (54) is arranged at a defined distance from the piston head-side end of one of the drive cylinders (24). This correcting sensor can be temporarily activated for initiating a reversing process overruling the rod-side position sensor (52";) of the other drive cylinder (24";).