An electrical connector assembly mounted on a printed circuit board (PCB) includes an insulating housing. The insulating housing includes a base with opposite front and rear end regions and a plurality of side walls upwardly extending from the base. The base cooperates with the side walls to commonly define a first receiving room. A notch defined in the front region of the base forms a second receiving room under the first receiving room. Said second receiving room is smaller than the first receiving room in both the front-to-back direction and a transverse direction perpendicular to said front-to-back direction. No portions of said contacts are located in the second receiving room so as to allow an optoelectronic module including a first portion and a second portion to be snugly received in the first receiving room and the second receiving room respectively, the second portion is attached to the first portion and supported on a top surface of the PCB.