An electrical connector includes an insulative housing, a number of contacts retained in the insulative housing and a metal shell enclosing the insulative housing. The metal shell includes a top wall defining a pair of slits each extending along a transverse direction, a cutout communicating with the slits and a L-shaped cantilevered arm residing in the slits and the cutout. The cantilevered arm includes a base portion protruding along the transverse direction and situated between the pair of slits and a deformable arm extending into the cutout along a mating direction perpendicular to the transverse direction. The deformable arm comprises a locking protrusion bent upwardly for locking with a notch of a mateable connector.