A conservative senator is praising the Obama administration for making what he says is a seemingly small but important improvement to the naturalization test issued by the Department of Homeland Security.

In 2015, Oklahoma Senator James Lankford began demanding that DHS change question 51 on the naturalization test, which describes the “two rights of everyone living in the United States” as including “freedom of worship.” The change, which will be on new naturalization forms by the end of 2016, will change “worship” to “religion.”

“I applaud the Department of Homeland Security for listening to me and deciding to change their material to reflect our First Amendment right of freedom of religion,” said Lankford. “At first glance, it appears like a small matter, but it is actually an important distinction for the Constitution and the First Amendment.”

In June, Lankford sent a letter to DHS Secretary Jeh Johnson about the issue, noting that to his knowledge, DHS replaced “freedom of religion” language in 2008 because it was determined “worship” was more inclusive than “religion.”

Lankford, a former Baptist pastor, said in his press release that the one-word difference is key:

The “freedom of religion” language reflects our right to live a life of faith at all times, while the “freedom of worship” reflects a right simply confined to a particular space and location. We live in a great nation that allows individuals to live out their faith, or have no faith at all. To protect freedom and diversity, we must carefully articulate this right throughout the federal government.

The conservative Republican has made religious liberty a top priority of his time in the Senate. Earlier this year, Lankford led 206 Members of Congress in signing an amicus brief to the Supreme Court defending the rights of religious non-profits to not be forced to provide insurance coverage for contraceptives and abortifacients.

A day later, Lankford invited the president of Oklahoma Wesleyan University, one of the plaintiffs suing the government over the insurance mandate, to be a guest during President Obama’s last State of the Union address.

The DHS naturalization issue has been a project of the freshman senator’s for nearly a year. On April 29 of last year, he addressed it during a question-and-answer session during Jeh Johnson’s testimony to the Senate Homeland Security and Government Affairs Committee.