This paper examines the diachronic origin of a vowel split in the Bantu language Hungan. It is shown that the inherited Proto-Bantu seven-vowel (7V) system was first reduced to a classical five-vowel (5V) system before the Kipuka variety of Hungan developed a new kind of 7V system. Such a 7V>5V>7V cycle has never before been described in Bantu. The new 7V system is thus the end product of a vowel merger and a vowel split which succeeded each other, but it could be mistaken for the outcome of a chain shift. The vowel split itself started out as an internally-motivated allophonic variation between tense and lax mid vowels that subsequently became phonologized through an externally-motivated loss of the conditioning environment. It can therefore be considered as a contact-induced language-internal change.