Index: src/wp-admin/includes/ajax-actions.php
===================================================================
--- src/wp-admin/includes/ajax-actions.php	(revision 28155)
+++ src/wp-admin/includes/ajax-actions.php	(working copy)
@@ -2233,7 +2233,7 @@
 		wp_send_json_error();
 	}
 
-	$update_php = self_admin_url( 'update.php?action=install-theme' );
+	$update_php = network_admin_url( 'update.php?action=install-theme' );
 	foreach ( $api->themes as &$theme ) {
 		$theme->install_url = add_query_arg( array(
 			'theme'    => $theme->slug,