Abstract: The present invention is directed toward a locking mechanism for aiding in the prevention of accidental or unintentional disengagement of the nozzle assembly from a needleless injection device. In one embodiment of the locking mechanism, a stud positioned on the nozzle assembly engages a recess in the injector to help to deter the nozzle assembly from rotating during firing of the injector. In another embodiment of the locking mechanism, a nib on the nozzle assembly engages a recess in the injector to deter the nozzle assembly from rotating during firing of the injector. A retaining element may be utilized within the injector to provide the recesses for engagement with the locking mechanisms.