The title compound, C(18)H(10)O(4), has been isolated as an impurity in commercially available 6,11-dihydr-oxy-5,12-naphth-acenedione. The title compound exhibits yellow fluorescence in the solid state. The mol-ecule has crystallographic inversion symmetry and is planar, with an r.m.s. deviation of 0.031 (1) Å. The crystal structure is stabilized by C-H⋯O hydrogen bonds and π-π stacking inter-actions between 3-methyl-eneisobenzofuran-1(3H)-one units [inter-planar distance 3.43 (1) Å].