|Abstract:||Affix vowels often alternate to agree with stem vowels in a pattern dubbed root-outward harmony. I propose that root-outward harmony is subject to a condition that a stem not be phonologically altered under affixation. This analysis accounts most parsimoniously for the core empirical generalization of root-outward harmony: that stem vowels never alternate to agree with affix vowels even if the only alternative is for stem and affix to disagree. Analyses in terms of underspecification and/or directionality capture this generalization less readily. I formalize the proposed analysis in terms of stem-affixed form faithfulness in Optimality Theory and compare it with likely alternatives.