Laboratory experiments have demonstrated that a mass-independent fractionation (MIF) signature is present in elemental sulfur produced during SO2 photolysis, but the underlying mechanism remains unknown. I report here the results of chemical kinetics modeling of self-shielding during photodissociation of SO2 in the over(C, ̃)1 B2 - over(X, ̃)1 A1 bands from 190 to 220 nm. This band system is dominated by a bending mode progression that produces shifts in the absorption spectrum upon sulfur isotope substitution. Self-shielding in the rotationally-resolved lines of 32SO2 produces MIF signatures in SO and residual SO2. Using approximate synthetic spectra for the sulfur isotopologues of SO2, I show that SO2 photolysis yields a sulfur MIF signature that can account for much of the laboratory MIF measured, and is in qualitative agreement with Δ33 S and Δ36 S values observed in Archean rocks.