Proofreading one's own writing is difficult due to the overfamiliarity of one's writing, which has been claimed to conceal errors, even extraneous errors inserted by someone else (as in collaborative writing). In the present research, we examined whether increasing one's familiarity with text can indeed have a negative influence on error detection. Participants were asked to identify word errors in different contexts: a passage that was unfamiliar, previously read, copied, memorised or paraphrased. These tasks represented a continuum of progressively more demanding and time-consuming activities, which were thought to lead to comparable increases in text familiarity. Greater familiarity with the text to be proofread was expected to improve its predictability and thus the likelihood of overlooking errors. In agreement with the level-of-familiarity account, as the delay between memorising and proofreading increased so did the proportion of errors detected per minute. (Contains 1 table.)