It is proposed that failure to consistently produce inflectional morphology by Mandarin-speaking learners of English is due to properties of the LI prosodic phonology which are transferred into the interlanguage grammar. While English requires inflection to be adjoined to the Prosodic Word, Mandarin does not permit this structure. Inflection in Mandarin is instead incorporated into the PWd of the stem to which it attaches. It is shown that Mandarin speakers fall into two groups in their treatment of English inflectional morphology. One group of learners is sensitive to the need for a unified analysis of inflection. They recognize that English does not permit a stem-internal analysis of this morphology, but as their grammars do not permit adjunction, inflection is deleted across-the-board. For the other group, inflection surfaces variably, for those stimuli where the shape of the stem enables it to be incorporated into the PWd, as in the L1.