Judge rules Kansas cannot require citizenship proof to vote

Ok, let's try to understand this. Only citizens are allowed to vote, but it's illegal to require proof that they are eligible to vote? How does this even compute?

WICHITA, Kan. –  A judge said Tuesday that Kansas can't require people to show proof of U.S. citizenship when registering to vote for federal elections at motor vehicle offices.

U.S. District Judge Julie Robinson ruled that the state's proof-of-citizenship requirements likely violate a provision in the National Voter Registration Act that requires only "minimal information" to determine a voter's eligibility. She ordered Kansas to register thousands of voters whose paperwork is on hold because they did not comply with the requirement.

http://www.foxnews.com/politics/2016/05/18/judge-rules-kansas-cannot-require-citizenship-proof-to-vote.html