Nowadays, is widely accepted that functional size measurement is essential to manage and control software projects. In order to obtain early indicators for software projects, many functional size measurement procedures have been developed to measure the functional size of conceptual models. To do this, the measurement procedures assume that models do not present defects. However, this is an unreal assumption because, in practice, the conceptual models can have defects that may affect the implementation of final applications. This is especially important for software production processes based on MDD technology, where the conceptual models are key artifacts used as inputs in the process of code generation. Therefore, this paper presents how a functional size measurement procedure (which has been developed for the measurement of conceptual models of a specific MDD environment) can help in the detection of defects in conceptual models.