Models are key artifacts in Model-Driven Development (MDD) methods. To produce high-quality software by using MDD methods, quality assurance of models is of paramount importance. To evaluate the quality of models, defect detection is considered a suitable approach and is usually applied using reading techniques. However, these reading techniques have limitations and constraints, and new techniques are required to improve the efficiency at finding as many defects as possible. This article presents a case study that has been carried out to evaluate the use of a Functional Size Measurement (FSM) procedure in the detection of defects in models of an MDD environment. To do this, we compare the defects and the defect types found by an inspection group with the defects and the defect types found by the FSM procedure. The results indicate that the FSM is useful since it finds all the defects related to a specific defect type, it finds different defect types than an inspection group, and it finds defects related to the correctness and the consistency of the models.