Sales for Boeing Co.’s grounded 737 Max slipped in October after a prominent customer converted some of its orders for the narrow-body jet to twin-aisle 787 Dreamliners.

Boeing’s unfilled 737 order backlog, adjusted for accounting considerations, shrank by 19 aircraft during the month to 4,387 jets, the Chicago-based planemaker revealed on its website Tuesday.

The planemaker garnered negative 45 orders for the Max, net of cancellations and conversions, through the first 10 months of the year. Sales of the updated 737, the latest generation of a design dating to the mid-1960s, have largely halted since regulators imposed a global flying ban on the jet in March, after two fatal accidents killed 346 people.

Air Lease Corp., the largest publicly traded U.S. aircraft financier converted 15 of its Max orders to 5 of the carbon-composite Dreamliner, bolstering sales of the jet, Boeing spokesman Paul Bergman said.

Boeing notched 20 deliveries in October, including 12 Dreamliners and one previous-generation 737.