This article takes as its point of departure two complicating factors in a well-known sound change in Dutch: when vowels lengthened in open syllables, (i) a long mid vowel emerged for each of the high vowels; and (ii) the high and mid vowels in the front series merged when lengthened. As with many other sound changes, the traditional formulation of open syllable lengthening states only the terminal points of a development; it says nothing about the intermediate stages. This article visualizes at least three intermediate steps—diphthongization, prominence shift, and monophthongization—which offer a rationale for the lowering of the high vowels and the merger in the front series.