check for 0 division, stops parallax failing if only the single horizontal slide and multiple vertical

1 files changed, 1 insertions, 1 deletions

diff --git a/js/reveal.js b/js/reveal.js
index d2b2970..266df2c 100644
--- a/js/reveal.js
+++ b/js/reveal.js
@@ -2798,7 +2798,7 @@
 				horizontalOffsetMultiplier = config.parallaxBackgroundHorizontal;
 			}
 			else {
-				horizontalOffsetMultiplier = ( backgroundWidth - slideWidth ) / ( horizontalSlideCount-1 );
+				horizontalOffsetMultiplier = ( horizontalSlideCount-1  > 0) ? ( backgroundWidth - slideWidth ) / ( horizontalSlideCount-1 ) : 0;
 			}
 
 			horizontalOffset = horizontalOffsetMultiplier * indexh * -1;