When two orthographically similar words are displayed via (RSVP), the repeated letters in the second critical word are not detected, leading to a deficit in reporting this word known as repetition blindness (RB). In Turkish, letters containing diacritic markings, (e.g., ß, ö) are considered separate letters, yet are visually highly similar to their non-diacritic analogs (s, o). Four experiments used the phenomenon of RB to investigate whether diacritic letters are represented as more similar to their non-diacritic analogs than are two unrelated letters. The amount of RB for words differing by a single diacritic (ißim isim) was comparable to identical repeated words (isim isim), and was less than words differing by a visually unrelated letter (ißim ilim). Using an illusory words paradigm, readers migrated diacritics more frequently when RB was likely to be operating. Either RB is sensitive to visual similarity between letters, or diacritic letters are mentally represented as variants of their non-diacritic analogue.