In the title co-crystal, C7H5NO4·C5H4N2O3, the two components are linked by an intermolecular hydrogen bond between the O—H and N—O groups [O⋯O 2.577 (3) Å]. The interplanar angle between the planes of the rings of the mol­ecules is 5.3 (2)°. The rings are stacked in the crystal with a mean interplanar distance of 3.279 (3) Å.