@@ -749,7 +749,7 @@ var Reveal = (function(){
// If we were on a vertical stack, remember what vertical index
// it was on so we can resume at the same position when returning
- if( previousSlide && previousSlide.parentNode.classList.contains( 'stack' ) ) {
+ if( previousSlide && previousSlide.parentNode && previousSlide.parentNode.classList.contains( 'stack' ) ) {
setPreviousVerticalIndex( previousSlide.parentNode, indexv );
}