The title compound, C(17)H(15)N(3)O(4)S, is a monoclinic polymorph with space group P2(1)/c of the previously reported triclinic form in P [Subashini et al. (2009 ▶). J. Chem. Crystallogr.39, 112-116]. In both polymorphs, intra-molecular O-H⋯N hydrogen bonds and dimer formation via a pair of inter-molecular N-H⋯N hydrogen bonds with an R(2) (2)(8) motif are observed. The two polymorphs differ in the next level of supra-molecular organization involving C-H⋯O hydrogen bonds with varied packing and different conformations.