Index: wp-admin/includes/screen.php
===================================================================
--- wp-admin/includes/screen.php	(revision 22080)
+++ wp-admin/includes/screen.php	(working copy)
@@ -387,7 +387,7 @@
 	 * @return WP_Screen Screen object.
  	 */
 	public static function get( $hook_name = '' ) {
-
+		global $hook_suffix;
 		if ( is_a( $hook_name, 'WP_Screen' ) )
 			return $hook_name;
 
@@ -398,7 +398,7 @@
 		if ( $hook_name )
 			$id = $hook_name;
 		else
-			$id = $GLOBALS['hook_suffix'];
+			$id = $hook_suffix;
 
 		// For those pesky meta boxes.
 		if ( $hook_name && post_type_exists( $hook_name ) ) {