The U.S. Citizenship and Immigration Services (USCIS) will change its naturalisation test to include "freedom of religion" instead of "freedom of worship" after a senator asked the agency to update it.

Last year, U.S. Senator James Lankford wrote Secretary Jeh Johnson of the Department of Homeland Security, asking to change a question in the naturalisation test study materials that asks "What are the two rights of everyone living in the United States?"

"Freedom of worship" is listed among the choices instead of "freedom of religion."

Lankford said freedom of worship is inconsistent with the U.S. Constitution.

"Our forefathers came to America to have freedom of religion, not simply freedom of worship. Worship confines you to a location," he said, adding that freedom of religion is the right to exercise your religious beliefs.

USCIS Director Leon Rodriguez told Lankford in June last year that "there were no plans to change the naturalisation test or study materials."

But last March 30, Rodriguez wrote another letter to the senator to say that "upon further consideration, however, we have determined that making this change is feasible because it is a change in terminology rather than an addition or deletion of test content."

As such, Rodriguez said, the USCIS is revising its test study materials and web content. About 40 different internal and external web-based and printed publications will be revised to reflect the change.

Despite the impending change, the USCIS said "freedom of religion" and "freedom of worship" will be both considered as correct answers in the test.

Lankford applauded the DHS for its decision.

"At first glance, it appears like a small matter, but it is actually an important distinction for the Constitution and the First Amendment. 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," he said.