diff --git a/js/reveal.js b/js/reveal.js
index 4992a018..88bf4ac6 100644
--- a/js/reveal.js
+++ b/js/reveal.js
@@ -1292,7 +1292,7 @@
 			if( value === 'null' ) return null;
 			else if( value === 'true' ) return true;
 			else if( value === 'false' ) return false;
-			else if( value.match( /^[\d\.]+$/ ) ) return parseFloat( value );
+			else if( value.match( /^-?[\d\.]+$/ ) ) return parseFloat( value );
 		}
 
 		return value;