This article discusses the origin of the reading 'zry 'my help' in the text of the Great Isaiah scroll (Isa 49:5). The scroll is the oldest Hebrew copy of the Book of Isaiah. The author of the article proposes that variant 'zy 'my strength' (it might be translated also as 'my shelter'), which has been preserved in the Masoretic Text and in the scroll 1QIsa(b), should be considered as the original reading. The variant 'zry emerged as a result of harmonization Isa 49:5 with the texts from the Book of Psalms (10:14; 27:9; 30:11; 63:8) and the Book of Isaiah (41:10, 13, 14; 44:2). This process was facilitated by the following circumstances: first, the words 'zr and 'z are paronyms, second, at the end of the first millennium B. C. E. they were perceived as synonyms.