This short note is intended as a supplement to Jensen's fine structure paper [2]. Its purpose is to correct an error in that paper, and in so doing describe the precise relationship between the Jensen hierarchy of constructible sets and the more usual hierarchy of constructible sets. We did not observe this mistake when we wrote our account of Jensen's work in our monograph [1], so we feel that, despite the relative simplicity of the correct proof of the correct result, we should put the record straight once and for all.