A fastening member for securing a rearview mirror housing to a vehicle and a related rearview mirror assembly are disclosed. The housing has a mirror carrier plate secured therein and defining an opening extending through the housing, the mirror carrier plate including at least one fastening connector disposed adjacent the opening. The fastening member includes a first support arm having a first end and a second end, the first end of the first support arm for securing to the vehicle, a second support arm having a first end and a second end, the first end of the second support arm for securing to the vehicle, the second support arm extending substantially parallel to the first support arm, and a connecting piece extending substantially perpendicular to the first and second support arms and formed integrally with the first and second support arms. The connecting piece includes at least one fastening connector disposed thereon for connection to the at least one fastening connector disposed on the mirror carrier plate to secure the housing to the fastening member and thereby to the vehicle. The fastening member may be formed of plastic, and the connecting piece may extend perpendicularly beyond at least one of the support arms.