An electrical connector assembly includes an insulative housing (1) with a plurality of terminal passages (12), a plurality of contacts (2) received in the corresponding terminal passages, and a shell (5) enclosing the insulative housing. The shell has a top shell (51) and a bottom shell (52) assembled with each other, the bottom shell comprises a frame-shaped base portion (520) and an extension portion (523) extending backwards and bent downwards from the base portion. The base portion defines a top wall (5201), a bottom wall (5202) and a pair of side walls (5203) connecting with the top wall and the bottom wall, the extension portion has a bottom surface lower than the bottom wall of the base portion and a pair of side portions bent upwards from lateral edges of the bottom surface, the side walls of the base portion and the side portions of the extension portion have a locking mechanism engaging the base portion with the extension portion.