This paper presents a partially-automated solution for the definition of test oracles for validating Simulink models. Since these models are widely used for the design of embedded systems, their thorough validation is key. Errors and misunderstandings in these models may preclude the correctness and reliability of the final system: a manual, human-intensive validation activity is not enough, and automated solutions are fundamental to improve the current state of the art. The paper also presents Apolom, a prototype oracle generator, and the results of two experiments.