The subject application relates to blade root wedging lock in a circumferential groove in a rotor such as the drum of an axial turbomachine compressor. The body (32) of the lock includes a solid portion (38) designed to be housed in the groove and having two opposite bearing surfaces (40) and at least one circumferential wedging surface (42). The body (32) further includes an upper portion (36) in the shape of an elongated generally vertical chamber designed to be flush with the upper surfaces of the platforms of adjacent blades when the lock is correctly positioned. This chamber (36) is truncated (44) so as to reduce its length in a direction perpendicular to the circumference, corresponding to the axis of rotation of the rotor. The lock can thus be accommodated in a narrow groove without decreasing the diameter of the clamping screw passing through the hole (34). The subject application also relates to a rotor and a turbomachine equipped with the lock.