Pyridine-4-carbaldehyde–fumaric acid (2/1)

In the title co-crystal, 2C₆H₅NO·C₄H₄O₄, two crystallographically different hydrogen-bonded trimers are formed, one in which the components occupy general positions, and one generated by an inversion centre. This results in the uncommon situation of Z = 3 for a triclinic crystal. In the formula units, mol­ecules are linked by O—H...N hydrogen bonds.