In an aspect, the present disclosure includes a method, apparatus, and computer readable medium for wireless communications for configuring of a NAS COUNT value of a mapped EPS security context associated with an intersystem change of a UE from a 5G system to an EPS. The aspect includes generating, by a UE, a mapped EPS security context associated with an intersystem change of the UE from a 5G system to an EPS, wherein the mapped EPS security context comprises security parameters created based a 5G security context used for the 5G system, the security parameters enabling security-related communications between the UE and a network entity; determining an UL NAS COUNT value and the DL NAS COUNT value for the mapped EPS security context; and transmitting, by the UE, a NAS message to the network entity, the NAS message including the UL NAS COUNT value of the mapped EPS security context.