Significance Photosystem II (PSII) is a multisubunit membrane protein complex that catalyzes light-driven oxidation of water, supplying energy to nearly all life on Earth. Because of the challenging chemistry it performs, PSII undergoes frequent damage, prompting an intricate cycle of disassembly, repair, and reassembly. Psb28, a protein that binds transiently to the RC47 intermediate complex, protects PSII from light-induced damage. The location of Psb28 in PSII has not been determined. In this study, we used chemical cross-linking, mass spectrometry, and protein docking to demonstrate that Psb28 binds to cytochrome b ₅₅₉ . Our results allow us to propose a mechanism by which Psb28 exerts its protective effect on the vulnerable RC47 complex.