The new U.S. defense secretary, James Mattis, called NATO Secretary General Jens Stoltenberg Monday — a gesture of good will on his first day in office that will raise the spirits of officials in Brussels, who were deeply unsettled by President Donald Trump’s rhetoric describing the transatlantic alliance as “obsolete.”

Trump, both on the campaign trail and during his transition into office, had raised questions about America’s commitment to NATO’s core principle of collective defense, suggesting America’s support might waver if allies did not sufficiently carry their own weight by paying a fair share of costs.

Mattis, a retired Marine Corps general whose nickname is “Mad Dog,” had voiced a much different view during his Senate confirmation hearing, calling NATO “the most successful military alliance in modern world history.” He also said, “If we did not have NATO today, we would have to create it.”

Mattis was one of just two Trump cabinet nominees confirmed by the U.S. Senate on Friday, Trump’s inauguration day. The other, Homeland Security Secretary John F. Kelly, is also a former Marine Corps general.

According to a NATO read-out of Monday’s call, Stoltenberg congratulated Mattis on his appointment and the two “agreed on the fundamental and enduring value of NATO for the security of both Europe and North America.” They also discussed pushing for increased military spending by NATO allies and stepping up counter-terrorism efforts.

In a statement, Stoltenberg said, “I had an excellent discussion with Secretary Mattis today — a strong friend of NATO at the Pentagon. Secretary Mattis knows the Alliance’s value well, having been NATO’s Supreme Allied Commander for Transformation. I look forward to welcoming him back to the NATO family, and to seeing him at our next meeting of defense ministers in February.”