The isospin mixing was deduced in the compound nucleus ^{80}Zr at an excitation energy of E^{*}=54 MeV from the γ decay of the giant dipole resonance. The reaction ^{40}Ca+^{40}Ca at E_{beam}=136 MeV was used to form the compound nucleus in the isospin I=0 channel, while the reaction ^{37}Cl+^{44}Ca at E_{beam}=95 MeV was used as the reference reaction. The γ rays were detected with the AGATA demonstrator array coupled with LaBr_{3}:Ce detectors. The temperature dependence of the isospin mixing was obtained and the zero-temperature value deduced. The isospin-symmetry-breaking correction δ_{C} used for the Fermi superallowed transitions was extracted and found to be consistent with β-decay data.