The missing link: Studies on the biosynthesis of riboflavin have failed to characterise dephosphorylation of the intermediate 5‐amino‐6‐ribitylamino‐2,4(1H ,3H )‐pyrimidinedione 5′‐phosphate. We show that this reaction can be catalysed in Escherichia coli by YigB and YbjI and in plant chloroplasts by AtcpFHy1, which are members of the haloacid dehalogenase superfamily.