Dahl's law is a sound rule in some of the Northeast Bantu languages that illustrates a case of voicing dissimilation. In the history of these languages, a voiceless stop, such as, became voiced when immediately followed by a syllable with another voiceless stop. For example, Nyamwezi has -datu "three" where Swahili, a Bantu language that did not undergo Dahl's law, has -tatu, and Shambala has mgate "bread" where Swahili has mkate. Dahl's law is the reason for the name Gikuyu when the language prefix normally found in that language is ki-.