Grammatical affix undergoing phonetic erosion is sometimes abruptly replaced by a conveniently-available lexical stem sharing one or more phonological segments. The new affix has phonological shape of the old independent stem, but acquires basic grammatical function of the old affix. Because the old affixal form is eliminated, the historical process is easily misdiagnosed. This is illustrated in Uto-Aztecan. (Author/MSE)