Methodologies to conjugate proteins to property-enhancing entities are highly sought after. We report a remarkably simple strategy for conjugating proteins bearing accessible cysteines to unprotected peptides containing a Cys(Scm) protecting group, which is introduced on-resin via a Cys(Acm) building block. The peptides employed for this proof of principle study are highly varied and structurally diverse, and undergo multiple on-resin decoration steps prior to conjugation. The methodology was applied to three different proteins, and proved to be efficient and site-selective. This twist on protecting group chemistry has led to a novel and generally applicable strategy for crossed-disulfide formation between proteins and peptides.