diff --git a/js/reveal.js b/js/reveal.js
index 4f9c2844..16d7fa9a 100644
--- a/js/reveal.js
+++ b/js/reveal.js
@@ -484,8 +484,8 @@ export default function( revealElement, options ) {
 		dom.wrapper.setAttribute( 'data-background-transition', config.backgroundTransition );
 
 		// Expose our configured slide dimensions as custom props
-		dom.viewport.style.setProperty( '--slide-width', typeof config.width == 'string' ? config.width :  config.width + 'px' );
-		dom.viewport.style.setProperty( '--slide-height', typeof config.height == 'string' ? config.height :  config.height + 'px' );
+		dom.viewport.style.setProperty( '--slide-width', typeof config.width === 'string' ? config.width :  config.width + 'px' );
+		dom.viewport.style.setProperty( '--slide-height', typeof config.height === 'string' ? config.height :  config.height + 'px' );
 
 		if( config.shuffle ) {
 			shuffle();