A locking device is provided that is configured to be attached to the MPO connector module and placed in a locking state that prevents the MPO connector module from being decoupled from the receptacle. The locking device may be a locking clip that is configured to be inserted into a keying slot formed in an MPO connector module. When the locking clip is inserted into the keying slot and placed in a locking state, the locking clip prevents the MPO connector module from being decoupled from the receptacle. If the locking clip is placed in an unlocking state, a tool or fingers can be used to extract the locking clip from the keying slot, thereby making it possible to decouple the MPO connector module from the receptacle.