diff --git a/lib/OpenLayers/BaseTypes.js b/lib/OpenLayers/BaseTypes.js
index 20de23cd7e..d156d61a1b 100644
--- a/lib/OpenLayers/BaseTypes.js
+++ b/lib/OpenLayers/BaseTypes.js
@@ -756,7 +756,7 @@ OpenLayers.Element = {
       }
     }
 
-    if (window.opera && ['left', 'top', 'right', 'bottom'].include(style))
+    if (window.opera && OpenLayers.Util.indexOf(['left', 'top', 'right', 'bottom'],style) != -1)
       if (OpenLayers.Element.getStyle(element, 'position') == 'static') value = 'auto';
 
     return value == 'auto' ? null : value;