The asymmetric unit of the title compound, C(12)H(11)NO(4), contains two mol-ecules. In the crystal, neighbouring mol-ecules are linked together by O-H⋯O hydrogen bonds into dimers. The dimers are arranged into columns parallel to the a axis, meditated by π-π inter-actions [centroid-centroid distances = 3.856 (3) and 3.857 (3) Å]. The crystal structure is further stabilized by weak inter-molecular C-H⋯O inter-actions. The crystal studied was a non-merohedral twin with a ratio of the twin components of 0.657 (11):0.343 (11).