diff --git a/src/core.js b/src/core.js
index 0913e08..d330555 100644
--- a/src/core.js
+++ b/src/core.js
@@ -278,7 +278,7 @@ $.extend( $.validator, {
 				38, 39, 40, 45, 144, 225
 			];
 
-			if ( event.which === 9 && this.elementValue( element ) === "" || excludedKeys.indexOf( event.keyCode ) !== -1 ) {
+			if ( event.which === 9 && this.elementValue( element ) === "" || $.inArray( event.keyCode, excludedKeys ) !== -1 ) {
 				return;
 			} else if ( element.name in this.submitted || element === this.lastElement ) {
 				this.element( element );