This paper rejects Matsumoto's (1984, 1995) arguments that o_1 and o_2 in Old Japanese (OJ) are allophones of the phoneme /o/. Matsumoto claims that a restricted distribution of the phonetically unmarked o_1, its low frequency, and the anomalous direction of its merger with o_2 should be regarded as denoting their status as allophones, rather than two different phonemes. The phonological distinction of vowel quantity in OJ and pre-OJ, and Short-mid-vowel-raising in pre-OJ (Hattori 1976, 1979a, b) and Vowel-shortening, which shortens the vowel of the first syllable in a disyllabic morpheme containing two long vowels in pre-OJ, can explain all the alleged anomalies and serve to invalidate Matsumoto's arguments.