Curable RTV-1 organopolysiloxane compositions which maintain the properties and adhesive strength even in hot moist conditions include a bis-hydroxyl-functional organopolysiloxane, an organosilicon compound comprising an α-alkoxysilane bonded through a methylene group to a heteroatom of a heterocyclic compound, and a branched, non-resinous alkoxyfunctional organopolysiloxane containing at least 20 mol percent of R5SiO3/2 moieties where R5 is a hydrocarbyl radical.