The news that someone on the U.S. government's terrorist watch list could buy a one-way ticket with cash and board a U.S.-bound aircraft with hidden explosives came as a shock to many Americans.

Here's something equally shocking: Lawful residents of the U.S. who are on the watch list are permitted to buy or possess firearms under federal gun control laws.

Felons can't legally buy guns. Neither can the mentally ill or nine other classes of individuals who are ineligible to own firearms. But if you're on the terrorist watch list, no problem.

Assuming Umar Farouk Abdulmutallab had obtained a valid tourist or student visa and could establish his residency in a state for 90 days, in theory he could have legally purchased a weapon from a federal firearms licensee.

That shouldn't be the case. But an audit released by the Government Accountability Office last summer revealed that people on the terrorism watch list were able to purchase guns in 865 of 963 attempts over a five-year period beginning in 2004.

The National Rifle Association has opposed congressional efforts to plug the watch-list loophole. An NRA lobbyist told the Washington Post the group's opposition was based on a Justice Department inspector general's report that found about 6 percent of the people on the list were included for outdated or erroneous reasons.

Problems involving the accuracy of the terror watch list need to be addressed, as the circumstances surrounding the attempted bombing of Flight 253 make clear. But those imperfections shouldn't be the enemy of common-sense public safety.

The GAO report doesn't even call for automatically blocking all sales to individuals on the watch list. It merely recommends giving the U.S. attorney general the flexibility to deny firearm purchases to subjects on the terror watch list when “information suggests the purchase could pose a threat to national security.”

As the events of Christmas Day demonstrate, terrorists will continue to try to exploit laws and procedures intended to safeguard the American people. There's no reason to provide them with an assist by allowing terror-watch subjects to have broad, legal access to firearms.