The title compound, C14H12O4, forms crystals which appear monoclinic but are actually twinned triclinic. The asymmetric unit consists of two similar molecules, which differ only in the conformation of the 3-oxobutyl side chain. The molecular conformation is characterized by an intramolecular O-H...O hydrogen bond between the hydroxy group and the adjacent carbonyl O atom. The crystal structure is stabilized by O-H...O hydrogen bonds connecting the molecules into zigzag chains running along the b axis.