Although combining methods is nothing new, more contributions about why and how to mix methods for validation purposes are needed. This article presents a case of validating the inferences drawn from the Participatory Evaluation Measurement Instrument, an instrument that purports to measure stakeholder participation in evaluation. Although the process was intended to be almost exclusively quantitative, one of its components unexpectedly turned into a mixed methods study. This, in turn, spurred on a cycle of instrument revision and further quantitative validation. Whereas the validation evidence is modest and tentative, it suggests that the revised version of the Participatory Evaluation Measurement Instrument offers a better fit with the respondents’ opinions regarding the participation level of selected evaluation cases. The article concludes with a brief discussion on the added value of mixed methods for validation purposes.