Purpose - The purpose of this study is to propose and model an integrated production-maintenance strategy for unreliable production systems producing conforming and non-conforming items. Design/methodology/approach - The proposed integrated policy is defined and modeled mathematically. Findings - The paper focuses on finding simultaneously the optimal values of the lot size Q and the age T at which preventive maintenance must be performed. These values minimize the total average cost per time unit over an infinite horizon. Practical implications - The paper attempts to integrate in a single model the three main aspects of any manufacturing system: production, maintenance, and quality. It deals with the lot-sizing problem for a production system which may randomly shift to an out-of-control state and produce non-conforming units. The system is submitted to an age-based preventive maintenance policy. The effect of performing preventive maintenance on quality- and inventory-related costs is shown through a numerical example. Originality/value - The paper proposes an integrated model that links EMQ, quality and an age-based preventive maintenance policy. It is shown that performing preventive maintenance yields reduction in inventory- and quality-related costs.