A device for fabricating a composite material part by injecting resin into a fiber structure. The device includes: a first die presenting two adjacent support surfaces defining a reentrant angle between them; at least one chock with a wedge-shaped portion configured to press the fiber structure into the angle; and a second die movable relative to the first die, the first and second dies being configured to clamp on the fiber structure and the chock. The chock is connected to the second die by at least one link, the link being hinged relative to the second die and relative to the chock to guide the wedge-shaped portion towards the angle to press the fiber structure into the angle when the second die approaches the first die.