Latin American operator Avianca has converted orders for five Airbus A319neo jets to the larger A320neo.
Analysis of the airframer's latest backlog data, covering April 2017, reveals the switch.
Avianca is the largest customer for the A319neo, which has been the weakest-selling model in the re-engined family.
It lifted its commitment to the variant to 28 a year ago, by converting nine A320neo orders, but switched three back in December. The swap of another five last month leaves the Latin American operator with orders for 20 of the type.
US carrier Frontier Airlines accounts for another 18 A319neos, with the remaining 12 orders split between unidentified customers and business jet specialists.
The A319neo carried out its maiden flight at the end of March this year, commencing its certification effort.
Analysis of Airbus's single-aisle business over April also shows that Chinese lessor CALC cancelled a pair of A320neos, while an undisclosed customer cancelled a further four.