It is believed that traditional asymmetric cryptosystems are compromised and symmetric cryptography can be used in the post-quantum world. In this paper, a new model based on post-quantum a set of FLAT (PQ-FLAT) protocol is proposed to ensure security in the machine to machine communication with post-quantum cryptography and it is inspired by the federated lightweight authentication of things (FLAT) protocol, which works effectively for resource-constrained devices in machine to machine (M2M) communication systems. The proposed model includes resource-constrained devices, certificate provider (CP), and service provider (SP). Communication of the certificate provider between resource-constrained devices is encrypted with AES. Instead of the asymmetric cryptography system between the certificate provider and the service provider, a lattice-based encryption mechanism, secure in the post-quantum world, is used. Thus, the FLAT protocol for resource-constrained devices is made resistant to post-quantum changes.