In this paper, we develop a joint quality control and preventive maintenance policy for a production system producing conforming and non-conforming units. The considered system consists of one machine which must supply another production line operating on a just-in-time basis. According to the proportion l of non-conforming units observed on each lot and compared to a threshold value lm, one decides to undertake or not maintenance actions on the system. In order to palliate perturbations caused by the stopping of the machine to undergo preventive maintenance or an overhaul, a buffer stock h is built up from the instant when the rejection rate reaches a threshold level lA in order to ensure the continuous supply of the subsequent production line. Our objective is to determine simultaneously the optimal rates View the MathML source and View the MathML source, and the optimal size h* which minimize the expected total cost per time unit including the average costs related to maintenance, quality and inventory.