Device-to-device (D2D) communications and cellular solutions represent key technologies for the development of a future infrastructure in which fifth-generation (5G) systems and the Internet of Things (IoT) will converge. A tricky issue to be carefully investigated in D2D communications is the prevention of threats to privacy and security caused by malicious devices. Thus, security mechanisms must be implemented in order to assure a reliable data exchange among involved devices. In this paper, we propose MtMS-sD2D (Machine-type Multicast Service with secure D2D), an architecture for the delivery of multicast traffic in an IoT scenario that takes advantage from D2D communications made reliable by means of a security mechanism. Furthermore, we discuss the procedures that must be followed to efficiently deliver multicast traffic. Finally, we provide some preliminary yet insightful simulation results .