Deselecting a value from a multiple select list box on a coldfusion form

I have a coldfusion form with a few multiple select list boxes. Users are successfully able select multiple values from any of those list boxes and do a search query that displays a results page. I realized though that if a user wants to deselect a value after they have selected it (before they click the search button) in any of the list boxes they cannot. How do you allow a user to deselect a value that was selected in a list box?