Cerro Mayo[1] or de Mayo is a mountain located in the Southern Patagonian Ice Field, in Santa Cruz Province, Argentina.

[2][3] Chilean cartography considered this mountain to be the true Cerro Stokes, the mountain first sighted by the Fitz Roy expedition and by the surveyors of both countries in the early 20th century (who considered Cerro Cervantes to be Stokes), and it was regarded as a border landmark until the 1998 agreement.

[5] After the signing of the 1881 Treaty between Argentina and Chile, the boundary in the area was defined in 1898 by the boundary surveyors, Francisco Pascasio Moreno from Argentina and Diego Barros Arana from Chile.

The boundary was defined by the following mountain landmarks and their natural continuity: Mount Fitz Roy, Torre, Huemul, Campana, Agassiz, Heim, Mayo, and Stokes (nowadays Cervantes).

[6][7][8][4] In 1998, the "Agreement between the Republic of Chile and the Republic of Argentina to determine the boundary line from Mount Fitz Roy to Cerro Daudet" was signed, defining section A and a small part of section B, with the area between Fitz Roy and the Murallón still pending.