A clip for retaining two planar elements assembled together on the main face thereof includes at least two side walls, each equipped with a groove opening and configured to enable the clip to be inserted on the two assembled planar elements and retain them against one another. At least one of the side walls is equipped with a slot opening into the groove and defining a flexible arm secured to the rest of the wall by a bending area. The free end of the flexible arm supports a stop partially blocking at least the groove.