The chief executive of Lockheed Martin Corp told President-elect Donald Trump on Friday that she was committed to driving down the cost of the company’s F-35 fighter jet, a day after Trump took aim at the cost of the F-35 in a Twitter post.

CEO Marillyn Hewson said she spoke with Trump on Friday afternoon and assured him that she had heard his message “loud and clear” about reducing the cost of the F-35.

Trump, in a tweet posted late on Thursday, suggested that an older aircraft made by rival aerospace company Boeing Co could offer a cheaper alternative to the F-35.

“Based on the tremendous cost and cost overruns of the Lockheed Martin F-35, I have asked Boeing to price-out a comparable F-18 Super Hornet!” Trump said.

Hewson, in a statement posted on Twitter, said she had had “a very good conversation” with Trump on Friday.

“I gave him my personal commitment to drive the cost down aggressively,” she said in the statement.

Lockheed shares closed down 1.3 percent on Friday, nearing their lowest levels since the Nov. 8 election. They were the biggest drag on a basket of defense-related stocks. Boeing’s stock ended near the unchanged mark.