The article deals with difficult cases of semantic differentiation of the verbs with the nedo- prefix and the verbs with the do- prefix - in the presence of a negation, and the orthography of verbs of this type. The accuracy of the verb nedostat’/nedostavat’ (in the meaning of ‘to be in insufficient quantity, not to be enough’) merged spelling solution, recorded by modern normative dictionaries and reference books, is being called into question.