Use of at least one toughness improver D for increasing the maximum linear expansion Max. elongation of a one-component thermosetting epoxy resin composition, wherein the one-component thermosetting epoxy resin composition comprises: a) at least one epoxy resin A having an average of more than one epoxy group per molecule; b) at least one latent curing agent for epoxy resins B; where the weight ratio of the at least one epoxy resin A having an average of more than one epoxy group per molecule to the at least one toughness improver D is 0.3-2.2, and wherein the toughness improver D is a terminally blocked polyurethane prepolymer of the formula: where R 1 is a p-valent radical of a linear or branched polyurethane prepolymer terminated by isocyanate groups after the removal of the terminal isocyanate groups; p has a value of 2 to 8; and R 2 is a blocking group which is detached at a temperature above 100°C, where R 2 is not a substituent selected from the group consisting of where R 12 is an alkylene group which has 2 to 5 carbon atoms and optionally has double bonds or is substituted, or is a phenylene group or a hydrogenated phenylene group, especially ε-caprolactam after removal of the NH proton; and R 19 represents bisphenols, after removal of a hydroxyl group, especially bisphenol A, bisphenol F and 2,2'-diallylbisphenol A, and wherein the maximum linear expansion Max. elongation is determined in a lap shear test during the cooling of a heated cured lap shear specimen, and wherein the maximum linear expansion Max. elongation is ≥ 2.145 mm, preferably ≥ 2.2 mm, preferably ≥ 2.5 mm, preferably ≥ 2.8 mm, preferably ≥ 3.0 mm, preferably ≥ 3.5 mm, preferably ≥ 4.0 mm, where the exact test method is defined in the description. a) at least one epoxy resin A having an average of more than one epoxy group per molecule; b) at least one latent curing agent for epoxy resins B; where the weight ratio of the at least one epoxy resin A having an average of more than one epoxy group per molecule to the at least one toughness improver D is 0.3-2.2, and wherein the toughness improver D is a terminally blocked polyurethane prepolymer of the formula: where R 1 is a p-valent radical of a linear or branched polyurethane prepolymer terminated by isocyanate groups after the removal of the terminal isocyanate groups; p has a value of 2 to 8; and R 2 is a blocking group which is detached at a temperature above 100°C, where R 2 is not a substituent selected from the group consisting of where R 12 is an alkylene group which has 2 to 5 carbon atoms and optionally has double bonds or is substituted, or is a phenylene group or a hydrogenated phenylene group, especially ε-caprolactam after removal of the NH proton; and R 19 represents bisphenols, after removal of a hydroxyl group, especially bisphenol A, bisphenol F and 2,2'-diallylbisphenol A, and wherein the maximum linear expansion Max. elongation is determined in a lap shear test during the cooling of a heated cured lap shear specimen, and wherein the maximum linear expansion Max. elongation is ≥ 2.145 mm, preferably ≥ 2.2 mm, preferably ≥ 2.5 mm, preferably ≥ 2.8 mm, preferably ≥ 3.0 mm, preferably ≥ 3.5 mm, preferably ≥ 4.0 mm, where the exact test method is defined in the description.