A clip for holding two flat elements joined together at their main face. The clip comprises a lower wall, an upper wall, and two side walls, the walls defining a closed volume. The side walls are provided with a groove having an end that opens into a face referred to as the “front face” of the clip. The grooves are configured to insert the clip by its front face onto the two joined flat elements and are each delimited by a contour having an upper segment and a lower segment opposite the upper segment. According to the present disclosure, the side walls each have, on their respective outwardly facing faces, a flat holding flange that extends along a rectilinear portion of the lower segment of the groove and provides a contact surface with one of the flat elements. The present disclosure also relates to an assembly comprising such a clip.