Condensation-crosslinkable compositions obtainable by use of organosilicon compounds having at least two OH groups, heterocyclic compounds of the formula A[CR 1 2 SiR a (OR 2) 3-a] x, where A represents a radical based on a heterocycle AH x, said radical containing one or more ring-forming elements of main groups 3 and/or 5 and having x hydrogen atoms replaced by chemical bonds to the CR 1 2 radical, wherein at least one of these bonds is situated on a ring-forming element of main group 3 or 5, R represents identical or different, monovalent, optionally substituted hydrocarbyl radicals, R 1 represents a hydrogen atom or monovalent, optionally substituted hydrocarbyl radicals and may be the same or different at each occurrence, R 2 represents monovalent, optionally substituted hydrocarbyl radicals and may be the same or different at each occurrence, a represents 0 or 1, preferably 0, and x represents 1, 2 or 3, preferably 1 or 2, more preferably 1, and/or partial hydrolyzates thereof and also at least one compound containing units of the formulae R 5 Si(OR 4) 2 O 1/2, R 5 Si(OR 4)O 2/2 and R 5 SiO 3/2, where R 4 at each occurrence independently represents an alkyl radical and may be the same or different, and R 5 at each occurrence independently represents a hydrocarbyl radical with the proviso that said compound contains at least 20 mol% of units of formula. organosilicon compounds having at least two OH groups, heterocyclic compounds of the formula A[CR 1 2 SiR a (OR 2) 3-a] x, where A represents a radical based on a heterocycle AH x, said radical containing one or more ring-forming elements of main groups 3 and/or 5 and having x hydrogen atoms replaced by chemical bonds to the CR 1 2 radical, wherein at least one of these bonds is situated on a ring-forming element of main group 3 or 5, R represents identical or different, monovalent, optionally substituted hydrocarbyl radicals, R 1 represents a hydrogen atom or monovalent, optionally substituted hydrocarbyl radicals and may be the same or different at each occurrence, R 2 represents monovalent, optionally substituted hydrocarbyl radicals and may be the same or different at each occurrence, a represents 0 or 1, preferably 0, and x represents 1, 2 or 3, preferably 1 or 2, more preferably 1, and/or partial hydrolyzates thereof and also A represents a radical based on a heterocycle AH x, said radical containing one or more ring-forming elements of main groups 3 and/or 5 and having x hydrogen atoms replaced by chemical bonds to the CR 1 2 radical, wherein at least one of these bonds is situated on a ring-forming element of main group 3 or 5, R represents identical or different, monovalent, optionally substituted hydrocarbyl radicals, R 1 represents a hydrogen atom or monovalent, optionally substituted hydrocarbyl radicals and may be the same or different at each occurrence, R 2 represents monovalent, optionally substituted hydrocarbyl radicals and may be the same or different at each occurrence, a represents 0 or 1, preferably 0, and x represents 1, 2 or 3, preferably 1 or 2, more preferably 1, and/or partial hydrolyzates thereof and also at least one compound containing units of the formulae R 5 Si(OR 4) 2 O 1/2, R 5 Si(OR 4)O 2/2 and R 5 SiO 3/2, where R 4 at each occurrence independently represents an alkyl radical and may be the same or different, and R 5 at each occurrence independently represents a hydrocarbyl radical with the proviso that said compound contains at least 20 mol% of units of formula. R 4 at each occurrence independently represents an alkyl radical and may be the same or different, and R 5 at each occurrence independently represents a hydrocarbyl radical with the proviso that said compound contains at least 20 mol% of units of formula.