According to the Comparative Tables, the primitive diphthongs [eu] and [iu] became [jō] and [jū] rather than becoming the diphthong [io] as they did in Ossiriandic (PE19/25). There was a similar development in Old Norse, where the diphthong [eu] broke into the triphthong [jɒu] and was later raised to [jō] (ref/@@@).