Bildts is a speech variety spoken by around 10,000 persons as a first or second language in the province Fryslân, in the north of the Netherlands. It is commonly claimed to be a dialect of Dutch containing some Frisian loan words. This article provides an analysis of Bildts based on a comparison of Bildts with its source languages: Frisian on the one hand and specific dialects of the province of South Holland on the other hand. It argues that Bildts combines a core lexicon mainly derived from Hollandic dialects with a grammar mainly derived from Frisian. However, the core lexicon also contains some Frisian words and the grammar has to some extent been levelled. The precise mixture is not easily described, let alone accounted for, in most models of language contact. Our approach combines sociological-historical information with linguistic factorisation in order to arrive at a plausible view of how Bildts came into existence. It is argued that Bildts is a mixed language, comparable to better known cases such as Ma’á, spoken in Tanzania, and that the specific nature of the mix involved the mutual accommodation of two groups of speakers: a group of mother tongue speakers of Frisian who acquired Bildts as a second language and a group of balanced bilingual speakers of Bildts and Frisian.