(Z)-3-(1-Hydroxy-3-oxobut-1-enyl)-6-nitro-2H-chromen-2-one

In the title compound, C13H9NO6, the coumarin system has the benzene ring aligned at 0.61 (18)° with respect to the pyrone ring. An intramolecular O—H...O hydrogen bond stabilizes the molecular conformation and a C—H...O contact also occurs. In the crystal, weak C—H...O interactions link the molecules, forming inversion dimers.