N-(3,4-Dichloro-phen-yl)maleamic acid.

The asymmetric unit of the title compound, C(10)H(7)Cl(2)NO(3), contains two unique mol-ecules, both being stabilized by an intra-molecular O-H⋯O hydrogen bond within their maleamic units. In the crystal structure, inter-molecular N-H⋯O hydrogen bonds link the mol-ecules into chains extending along [1] which are further assembled into sheets via short inter-molecular C-Cl⋯O=C contacts [3.102 (2) and 3.044 (2) Å].