diff --git a/include/dbstructure.php b/include/dbstructure.php
index 9faede0ca1..76ba37e37c 100644
--- a/include/dbstructure.php
+++ b/include/dbstructure.php
@@ -153,7 +153,7 @@ function update_structure($verbose, $action, $tables=null, $definition=null) {
 		} else {
 			// Drop the index if it isn't present in the definition and index name doesn't start with "local_"
 			foreach ($database[$name]["indexes"] AS $indexname => $fieldnames)
-				if (!isset($structure["indexes"][$indexname]) && substr($indexname, 0, 5) != 'local_') {
+				if (!isset($structure["indexes"][$indexname]) && substr($indexname, 0, 6) != 'local_') {
 					$sql2=db_drop_index($indexname);
 					if ($sql3 == "")
 						$sql3 = "ALTER TABLE `".$name."` ".$sql2;