On Tuesday, Boeing said that Miami-based 777 Partners had agreed to buy 30 more 737 MAX jets, virtually doubling the private equity firm's 737 MAX order book.
The contract, worth $3.7 billion at list prices, is a possible boost for the planemaker, which said last month that it had delivered 212 737 MAX jets this year despite production issues with its larger 787 aircraft.
In March, Boeing agreed to sell 24 737 MAX jets to 777 Partners, with an option to buy 60 more.
According to 777 Partners managing partner Josh Wander, the majority of the new order is for Boeing's 737-8-200 version.
Following the announcement, Boeing's stock increased by 1.5%.