diff --git a/src/core.js b/src/core.js
index cdd78517f4..611e5363bb 100644
--- a/src/core.js
+++ b/src/core.js
@@ -441,6 +441,10 @@ jQuery.extend({
 	},
 
 	inArray: function( elem, array ) {
+		if ( array.indexOf ) {
+			return array.indexOf( elem );
+		}
+
 		for ( var i = 0, length = array.length; i < length; i++ ) {
 			if ( array[ i ] === elem ) {
 				return i;