A cap for a fluid line connector having a male luer lock fitting, the cap having a first side and a second side opposite the first side, the cap comprising a barrier and a stopper extending axially from the barrier towards the first side of the cap. The barrier defines a keyway centred on a longitudinal axis. The shape of the keyway is configured to permit a correspondingly-shaped female luer lock fitting to pass axially therethrough to engage the male luer lock fitting of the fluid line connector. The stopper is configured to prevent rotation of the correspondingly-shaped female luer lock fitting in the first circumferential direction when a lug of the correspondingly-shaped female luer lock fitting is circumferentially aligned with the stopper.
