Sibilant harmony in Nkore-Kiga is an interesting problem case for agreement-based theories of harmony, particularly Agreement by Correspondence. Previous work reports that anteriority agreement is controlled by the rightmost sibilant in the stem, and also that the quality of a sibilant is allophonically determined by the following vowel. In such a system, it is impossible for surface-oriented agreement constraints to derive strictly right-to-left harmony. However, we show that Nkore-Kiga does not work in quite this way: sibilants are conditioned not allophonically, but by morphology. This allows the facts of this case to be explained within existing Agreement by Correspondence proposals.