Pope Francis smiles onboard the papal plane during his return to Rome, from Asuncion, Paraguay July 12, 2015 (Reuters/Alessandro Bianchi)

In one of his characteristically frank news conferences aboard the papal plane, Pope Francis promised on Sunday to read some of his American critics, particularly on the economy, in preparation for his trip to the United States in September.

“I have heard that some criticisms were made in the United States — I’ve heard that — but I have not read them and have not had time to study them well,” Pope Francis said, according to a report from the plane by the Catholic News Service.

Francis added that if he has “not dialogued with the person who made the criticism,” he doesn’t believe he has “the right” to comment on what they’re saying.

“I must begin studying these criticisms, no? And then dialogue a bit with this,” he added, according to the AP.

The pope did say, in response to a question from a reporter, that it was an “error” for him to not speak more about the needs and responsibilities of the middle class.

Here’s the exchange, as picked up by the New York Times:

“Thank you,” he replied, after a German journalist, Ludwig Ring-Eifel, asked about the omission. “It’s a good correction, thanks. You are right. It’s an error of mine not to think about this.”

[The wind won’t stop messing with Pope Francis’s look]

The pope was on his way back from a trip to South America, where he visited Ecuador, Bolivia and Paraguay. During the week-long trip, Francis gave a passionate address in Bolivia encompassing many social justice aspects of his approach to the papacy – the same sorts of remarks that some critics in the U.S. have characterized as too “anti-capitalist.”

“Do we realize that that system has imposed the mentality of profit at any price, with no concern for social exclusion or the destruction of nature?” Francis said in Spanish last week.

“We want change in our lives, in our neighborhoods, in our everyday reality. We want a change which can affect the entire world, since global interdependence calls for global answers to local problems. The globalization of hope, a hope which springs up from peoples and takes root among the poor, must replace the globalization of exclusion and indifference!” he continued, according to a translation from NBC News.

[Want tickets to see Pope Francis when he comes to the U.S.? Better start going to church.]

Francis also revisited some of the points present in his landmark encyclical on the environment. “Time, my brothers and sisters, seems to be running out; we are not yet tearing one another apart, but we are tearing apart our common home,” he said.

Pope Francis will visit Washington, D.C., New York and Philadelphia during his U.S. visit from Sept. 22-27, culminating with a mass at the World Meeting of Families conference in Philadelphia. Based on the pontiff’s schedule, it is expected that he will use the trip to discuss immigration and poverty in the U.S.