Yalaku is one of the smallest members of the Ndu language family of the Sepik region of New Guinea. Spoken in a hilly area off the Sepik river, Yalaku has been in intensive contact with the unrelated Kwoma for several generations. Comparison between Yalaku and closely related Manambu shows the presence of a number of grammatical patterns borrowed from Kwoma, alongside a number of loanwords. Tok Pisin, the lingua franca of Papua New Guinea, is known to every speaker of Yalaku, with the two languages in a diglossic relationship. Lexical loans from Tok Pisin are avoided; however, Tok Pisin impact is being felt in the pronunciation patterns by younger speakers, calques, and the presence of two borrowed grammatical forms–the possessive verb and the negator. Cultural and linguistic factors suggest an explanation for this seemingly curious development.