This article deals with some of the spelling changes that occurred in the 1640s. Many changes began before Meletius Smotrytsky’s Grammar was published in 1648, and the spelling rules of the Grammar 1648 were formed as a result of corrections in texts produced in the 1640s. At this time, demonstration of word border in writing manifested in clitics separation from autosemantic words, in the appearance of broad grapheme Є and Ѻ, and in changes in the spelling of the conjunction i. The stable orthographic opposition “beginning / not beginning of the word” begins to appear at this time as follows: in the beginning there were Є, Ѻ, ІА, not in the beginning-е, о, ѧ. The distribution of the graphemes ѹ/ȣ was associated with the accent and the position after the vowel o. The article also touches upon the appearance of the lexical homonyms ɪазыкъ ‘nation’-ѧзыкъ ‘tongue’ distinction, changes in the spelling of some borrowed words, and use of the letter Ѕ. Spelling changes of the 1640s are compared with the orthographic norms fixed in the various grammars, as well as in the advice of the Azbukovniks of the early 17th century.