Ninth-century Old English prose texts were composed by authors not famed for their linguistic skills and experienced a relatively long transmission until the end of the Anglo-Saxon period; unsurprisingly, they present a considerable number of authorial and scribal errors in the copies in which they survive. But editors of Old English texts have tended to discuss authorial translation errors individually, in textual notes, and often apologetically. Similarly, scribal errors are rarely studied in context, usually edited out of the modern edited text and at best confined to a textual apparatus. This article charts errors made by the author of the Old English Martyrology, who struggled to control his very considerable encyclopaedic knowledge in language often not conducive to accurate transmission; scribal errors arising from this language are also analysed. The authorial and scribal errors apparent particularly in the eleventh-century copies of this text point to a very difficult reading experience faced by readers in the late Anglo-Saxon period.