diff --git a/wp-admin/network/update.php b/wp-admin/network/update.php
index c7625b9a37..b2c6177fbc 100644
--- a/wp-admin/network/update.php
+++ b/wp-admin/network/update.php
@@ -7,6 +7,9 @@
  * @since 3.1.0
  */
 
+if ( isset( $_GET['action'] ) && in_array( $_GET['action'], array( 'update-selected', 'activate-plugin', 'update-selected-themes' ) ) )
+	define( 'IFRAME_REQUEST', true );
+
 /** Load WordPress Administration Bootstrap */
 require_once( './admin.php' );
 
diff --git a/wp-admin/update.php b/wp-admin/update.php
index 57d0cceaa8..8dd8a89bb2 100644
--- a/wp-admin/update.php
+++ b/wp-admin/update.php
@@ -6,8 +6,8 @@
  * @subpackage Administration
  */
 
-if ( isset( $_GET['action'] ) && in_array( $_GET['action'], array( 'update-selected', 'activate-plugin', 'update-selected-themes' ) ) )
-	define('IFRAME_REQUEST' , true);
+if ( ! defined( 'IFRAME_REQUEST' ) && isset( $_GET['action'] ) && in_array( $_GET['action'], array( 'update-selected', 'activate-plugin', 'update-selected-themes' ) ) )
+	define( 'IFRAME_REQUEST', true );
 
 /** WordPress Administration Bootstrap */
 require_once('./admin.php');