Index: wp-admin/admin.php
===================================================================
--- wp-admin/admin.php	(revision 21684)
+++ wp-admin/admin.php	(working copy)
@@ -41,6 +41,7 @@
 	do_action('after_db_upgrade');
 } elseif ( get_option('db_version') != $wp_db_version && empty($_POST) ) {
 	if ( !is_multisite() ) {
+		nocache_headers();
 		wp_redirect(admin_url('upgrade.php?_wp_http_referer=' . urlencode(stripslashes($_SERVER['REQUEST_URI']))));
 		exit;
 	} elseif ( apply_filters( 'do_mu_upgrade', true ) ) {
Index: wp-admin/upgrade.php
===================================================================
--- wp-admin/upgrade.php	(revision 21684)
+++ wp-admin/upgrade.php	(working copy)
@@ -17,6 +17,8 @@
 /** Load WordPress Bootstrap */
 require( '../wp-load.php' );
 
+nocache_headers();
+
 timer_start();
 require_once( ABSPATH . 'wp-admin/includes/upgrade.php' );