A system for rejection of tablets produced in a rotary tablet press comprises pan ejection nozzle for sorting out defective tablets. The ejection nozzle is supplied with compressed gas through a supply line having an inlet end for connection with a source of compressed gas and an outlet end communicating with the ejection nozzle. The supply line is provided with a control valve controlled by a control unit in order to open the supply line when a defective tablet has been detected by the control unit. Furthermore, the supply line is provided with a sensor arranged between the control valve and the inlet end of the supply line and adapted to detect a variable indicative of a gas flow through the control valve in order for the control unit to generate an error signal in the case of malfunction of the control valve.