This paper attempts to draw the attention of experts in Turkic linguistics to the mixed nature of the Old Turkic literary language. It is no surprise that an ancient literary language is linguistically not uniform, consisting as it does of artificial and clever amalgams, of words and forms taken from different dialects. This koiné phenomenon is known to different writing cultures. With regard to the Old Turkic koiné, the question of interest is which dialects were subject to amalgamation and which linguistic features allow us to distinguish between these dialects. As the article shows, it is the features described in Mahmud al-Kashgari’s Dīwān Luγāt at-Turk – a unique source on the Old Turkic dialect system, even if it is not fully comprehensive or complete – that help us to solve the problem.