An overpressure protection system (30) for a magazine (10) for storing explosive materials. The magazine (10) comprises a wall (12) which defines an internal chamber (14) for housing the explosive materials, with a first aperture (20) defined in the wall (12). The overpressure protection system (30) is configured to close the first aperture (20). The system (30) comprises a burst disc diaphragm (32) for covering the first aperture (20), and a protective cover (34) for locating outside of the chamber (14) and over the burst disc diaphragm (32). The protective cover (34) is spaced apart from the burst disc diaphragm (32) to form a cavity (38) with an opening (36) for venting fluid from the cavity (38).