In the title 2:1 adduct, C14H10O4S2·0.5C10H8N2O2, which arose from an unexpected oxidation of a precursor, the dihedral angle between the aromatic rings in the disulfide is 82.51 (11)°. In the crystal, the molecules are linked by O—H⋯O, O—H⋯N and C—H⋯O interactions, generating sheets.