The paper deals with the phenomenon of lexicalization (degrammaticalization) as a possible constraint on the standard secondary imperfectivation of Russian verb, which is regarded as the unique regular morphological mechanism of aspectual inflection. Several cases of lexicalization are discussed on the basis of an analysis of the material found in the Russian National Corpus -two cases of lexicalized plural noun forms (chasy 'clock' and kapli 'eyedrops') and two cases of secondary imperfectives (zaigryvat' 'flirt' and zamalchivat' 'hush smth up'). These cases of using lexicalized forms are discussed in comparison with corresponding non-lexicalized forms, if any, of standard plural (for the nouns above - 'hours' and 'droplets') and standard secondary imperfectives (for the verbs above - 'be starting to play' and 'be starting to get silent'). The analysis reveals two different possibilities: the parallel use of lexicalized and non-lexicalized forms (with lexicalized or non-lexicalized forms predominating) and the occurrence of lexicalized forms only (the case of zamalchivat'). The discussion leads to the conclusion that lexicalization significantly hinders standard secondary imperfectivation of prefixed Russian verbs.