In 1955, Lutovac argued that in the 16th century, the Slavic population of Opolje partially adopted Islam and partially emigrated elsewhere, and the vacancies created by emigration were filled by Albanian incomers. Dumbrowski in 2012 argued that the situation described by Lutovac led to language shift from Slavic to Albanian in Opolje and the surrounding region (but not Gora), and that this is the reason for what Dumbrowski argues is evidence of Slavic substrate effects in the Opoja Albanian dialect. Pulaha in 1984 noted that most Christians in Opolje in 1591 had Albanian names, which Dumbrowski interprets to indicate that at the time Opolje was switching from Slavic to Albanian, what Dumbrowski argues were the Albanian incomers had not yet been fully Islamized.