This talk aims to include in the study of loanwords not only phonological differences between borrowing and donor language, but also factors which may not depend solely on these differences, e.g. similarity, frequency and gradient grammaticality. The influence of these factors on the performance of English speakers in a shadowing task of Russian words with English-illegal initial clusters was tested. The frequency of potential adapted onsets in the English lexicon does not correlate with the strategy of adaptation. Judgments about the grammaticality of words containing illegal initial clusters and the similarity between pairs of words partially containing illegal onsets were obtained from English native speakers. The perceived grammaticality of a target cluster influenced performance in the shadowing task in the following ways: high-grammaticality target clusters were modified less often, and low-grammaticality clusters were mostly associated with vowel epenthesis. Similarity of an adaptation to a target was shown to be a predictor of its rate of use.