The present invention relates to reinforcement yarns coated with a sizing composition comprising at least one silane satisfying the formula: Si(R.sup.1)(R.sup.2)(R.sup.3)(R.sup.4) in which: R.sup.1, R.sup.2 and R.sup.3 are chosen from the following atoms or groups: --H (except in the case of R.sup.3), --Cl, --O--R.sup.5, --O--R.sup.6--O--R.sup.5, --O--(C.dbd.O)--R.sup.5, --O--R.sup.6--(C.dbd.O)--R.sup.5, R.sup.5 and R.sup.6 being chosen from hydrocarbon radicals whose main chain has from 1 to 4 carbon atoms; R.sup.4.dbd.--R.sup.7--NHR.sup.8 R.sup.7 being chosen from branched hydrocarbon radicals whose main chain has from 2 to 6 carbon atoms, R.sup.8 being chosen from the following groups: --H, --R.sup.9--NH.sub.2, --R.sup.10--NH--R.sup.9--NH.sub.2, R.sup.9 being chosen from hydrocarbon radicals containing 1 to 12 carbon atoms or from carbonyls, and R.sup.10 being chosen from hydrocarbon radicals whose main chain has from 1 to 6 carbon atoms. The glass yarns according to the invention are particularly suitable for reinforcing organic materials, the yarns and composites obtained resisting in a corrosive medium.