The formyl C-H thiolation of aldehydes using thiosulfonates using the decatungstate anion as a photocatalyst is reported. Using this photocatalytic protocol, both aromatic and aliphatic thioesters can be synthesized in good yields. The transformation consists of a cascade of double SH2 reactions, HAT and an ArS group transfer, and the yields are improved when the reaction is carried out in a CO atmosphere, which serves to limit the extent of decarbonylation acyl radicals that are generated in the reaction.