A fastening device for an electric control and/or indicator member, which includes a base, a fastening clamp fitted pivotably on the base about a first axis, the clamp including at least one branch having a free end designed to form at least a first bearing point against a wall, an element hinged about a second axis and interacting with the clamp to cause it to pivot about the first axis, a clamping screw for controlling the pivoting of the clamp, the clamp being configured in such a way that a first plane including the first axis and the second axis and a second plane including the first axis and the first bearing point form an angle of between 110° and 160°.