A connection element for bottom profile rails of a mounting system for photovoltaic modules, includes a base body (12) realized as a U-profile rail and having two parallel side legs (13) and a connection section (14), wherein both side legs (13) have a projection (16) on a free end (15) facing away from the connection section (14), the projection (16) being realized with the base body (12), wherein, in the mounted state, the side legs (13) are guided in channel sections (26) of the bottom profile rail (05) in such a manner that a wall of the channel sections (26) runs above the free ends (15) of the side legs (13), wherein the projection (16) is realized in such a manner that it does not project at the top beyond the wall of the channel sections (26) in the mounted state.