A connector assembly includes a receptacle connector and a plug connector. The receptacle connector includes a receptacle insulative housing including a receiving portion, a number of mating portions extending from the receiving portion and a number of contact-receiving slots extending through the mating portions and the receiving portion. At least one of the mating portions includes an anti-mismating block at a corner thereof. The plug connector includes a plug insulative housing including a mating surface and a number of cavities extending through the mating surface for receiving the mating portions. The plug insulative housing includes an anti-mismating groove at a corner of one of the cavities to receive the anti-mismating block of the receptacle insulative housing.