Parents at a high school near Dallas say the authors of a book on U.S. history misfired when they defined the Second Amendment -- and now one of the book's co-authors says the book is being revised.

The work book used at Guyer High School in the city of Denton, "The United States History: Preparing for the Advanced Placement Examination," includes the "summary" definition of the Second Amendment to include the right to "keep and bear arms in a state militia."

The edited definition is seen by gun-rights advocates as an affront to the Second Amendment, which states in full: "A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed."