A safety device for an injection device including a protective sheath driven by a spring, the safety device being capable of taking an injection configuration in which the sheath allows an injection needle to be left uncovered, and a safe configuration in which the sheath enables the injection needle to be covered; retractable catches for retaining the spring, the retractable catches retaining the spring under stress in such a manner as to hold the safety device in the injection configuration; and deactivation mechanism for deactivating the retractable catches, enabling the safety device to take a storage configuration in which the retractable catches are not subjected to stress from the spring.