jats:pAlthough John Towill Rutt's 1828 edition of the jats:italicDiary of Thomas Burton</jats:italic> remains a key source for the parliamentary history of the Cromwellian Protectorate, remarkably few historians – past or present – have paused to consider its limitations. This article offers the first thorough examination of Rutt's editorial practices to highlight a number of reasons why modern scholars should treat his edition with extreme caution. While touching upon those familiar debates concerning the appropriate use of parliamentary diaries in the early modern period, this article suggests that Rutt's editorial practices add further layers of complexity to how historians should approach his edition of Thomas Burton's diary. By focusing upon the debates of Richard Cromwell's parliament the second half of this article demonstrates how the over‐reliance of scholars upon Rutt's edition has helped to propagate a number of misconceptions about both the membership and nature of that parliament as a whole. The article concludes by recommending that historians approach Rutt's edition with far more care. In particular, it would be far better to return to Burton's manuscript diary and, where possible, to collate it with other surviving parliamentary diaries from this period.</jats:p>