To the copious list of peculiarities which single out Gascon among Occitan varieties (Carrera 2007) forms like "aso", "òmi" insteads of common Occitan "ase" 'donkey' and "òme" 'man' can readily be added. Such forms are nearly exclusively Gascon, although they are not used all over Gascony. Up to now they have not received a convincing explanation. Joan Seguy, before he published the Linguistic Atlas of Gascony, wrote : "the exasperating problem of the three different qualities i, e, u of the former stressless penult of Gascon has not found a solution yet" (Seguy 1950: 87). We suggest in the present paper to explain those Gascon forms by a well known Gascon salient feature, viz the fall of intervocalic -n-. Under such a hypothesis, the non co-inciding geographical distribution of forms in -o (as "aso") and in-i [i] (as "òmi") can be understood as the consequence of a well-type diffusion of linguistic change. The respective areas of each type of form result from a well of change for n-fall expandinɡ from west to east crossing an a well for final vowel deletion cominɡ from the east. As an extra advantage, the analysis presented here shed light on the existence of an area in Eastern Gascon where the final (unmarked) nasal has a coronal rather than velar realization: ([pˈan] "pan" 'bread' instead of [pˈaŋ] or [pã] elsewhere in Gascony.