According to the invention a safety device for a pre-filled syringe comprises a substantially cylindrical and hollow support body and a hollow needle shield slideably arranged relative to the support body. The support body comprises at least one resilient arm and the hollow needle shield or a needle shield assembly comprises at least one curved actuation ramp. The curved actuation ramp protrudes in a lateral direction (L) perpendicular to a central axis (A) of the safety device. The curved actuation ramp comprises a first lateral dimension (L1) at a proximal end of the needle shield and a second lateral dimension (L2) exceeding the first lateral dimension (L1) at a distal end of the needle shield. The resilient arm engages the curved actuation ramp when the needle shield is slid relative to the support body.