diff --git a/wp-admin/admin-header.php b/wp-admin/admin-header.php
index 27c496a710..bb8fe4ebd0 100644
--- a/wp-admin/admin-header.php
+++ b/wp-admin/admin-header.php
@@ -7,7 +7,8 @@
  */
 
 @header('Content-Type: ' . get_option('html_type') . '; charset=' . get_option('blog_charset'));
-if (!isset($_GET["page"])) require_once('admin.php');
+if ( ! defined( 'WP_ADMIN' ) )
+	require_once( 'admin.php' );
 
 get_admin_page_title();
 $title = esc_html( strip_tags( $title ) );