Index: src/wp-admin/includes/upgrade.php
===================================================================
--- src/wp-admin/includes/upgrade.php	(revision 32320)
+++ src/wp-admin/includes/upgrade.php	(working copy)
@@ -1564,7 +1564,7 @@
 
 	// 4.2
 	if ( $wp_current_db_version < 31351 && $wpdb->charset === 'utf8mb4' ) {
-		if ( ! ( defined( 'DO_NOT_UPGRADE_GLOBAL_TABLES' ) && DO_NOT_UPGRADE_GLOBAL_TABLES ) ) {
+		if ( ! defined( 'DO_NOT_UPGRADE_GLOBAL_TABLES' ) ) {
 			$wpdb->query( "ALTER TABLE $wpdb->usermeta DROP INDEX meta_key, ADD INDEX meta_key(meta_key(191))" );
 			$wpdb->query( "ALTER TABLE $wpdb->site DROP INDEX domain, ADD INDEX domain(domain(140),path(51))" );
 			$wpdb->query( "ALTER TABLE $wpdb->sitemeta DROP INDEX meta_key, ADD INDEX meta_key(meta_key(191))" );
@@ -2403,7 +2403,7 @@
 
 	// Upgrade versions prior to 4.2.
 	if ( $wp_current_db_version < 31351 ) {
-		if ( ! is_multisite() ) {
+		if ( ! is_multisite() && ! defined( 'DO_NOT_UPGRADE_GLOBAL_TABLES' ) ) {
 			$wpdb->query( "ALTER TABLE $wpdb->usermeta DROP INDEX meta_key, ADD INDEX meta_key(meta_key(191))" );
 		}
 		$wpdb->query( "ALTER TABLE $wpdb->terms DROP INDEX slug, ADD INDEX slug(slug(191))" );