Index: src/wp-admin/includes/upgrade.php
===================================================================
--- src/wp-admin/includes/upgrade.php	(revision 26249)
+++ src/wp-admin/includes/upgrade.php	(working copy)
@@ -2007,7 +2007,7 @@
  * @since 2.9.0
  */
 function pre_schema_upgrade() {
-	global $wp_current_db_version, $wp_db_version, $wpdb;
+	global $wp_current_db_version, $wpdb;
 
 	// Upgrade versions prior to 2.9
 	if ( $wp_current_db_version < 11557 ) {