Most production scheduling-related research generally assumes that a machine is able to process jobs continuously, and at all times. In practice, that is rarely the case; a machine may become unavailable during the production process due to random breakdown, preventive maintenance, or tool change necessitated by job mix or tool wear. For this reason, this paper investigates the problem of scheduling the processing of jobs and tool changes simultaneously. The objective is to minimize the total completion time of jobs. We first correct the existing model by Akturk et al. [2], and then we present four alternative models for an exact solution of the problem. Computational experiments are carried out to evaluate the efficiency of the models.