It has been observed that the trigger and target in labial harmony are sometimes required to share a particular feature. Working within the framework of Radical CV Phonology, I argue that labial harmony is always subject to further requirements, stated in terms of additional licensing relations. Radical CV Phonology uses a limited set of elements that can be involved in such licensing, resulting in a restricted typology of labial harmony. Furthermore, I propose a distinction between lexical elements, which are always visible, and elements derived through harmony, which become visible in cycles. Crucially, elements derived through labial harmony do not have access to elements derived through tongue-root harmony, thus accounting for the lack of labial harmony in high vowels in tongue-root harmony systems. This architecture also accounts naturally for the behaviour of /i/, which is opaque to labial harmony in Tungusic languages but transparent to labial harmony in Mongolic languages.