An electrical connector assembly comprises a first connector and a second connector. The first connector has a hood defining a mating opening. The second connector has a housing body configured to be received in the hood, a rear end wall formed continuous with the housing body and projecting outward from the housing body in a circumferential direction, a lock arm configured to prevent disengagement of the first connector and the second connector, and a cover disposed at the rear end wall covering a portion of the lock arm. A front end surface of the rear end wall facing the second connector forms a uniformly continuous flat surface in a region including the cover.