Organosilicon compounds each having in a molecule (A) a perfluoroalkyl group of at least 3 carbon atoms which may be separated by an etheric oxygen atom, (B) a monovalent hydrocarbon group containing a carboxylic acid anhydride structure, and (C) a hydrosilyl (SiH) group are novel and added to thermosetting elastomer compositions as adhesion aids whereby the compositions are improved in adhesion to various materials including metals, alloys, plastics, and ceramics.