diff --git a/htdocs/core/class/extrafields.class.php b/htdocs/core/class/extrafields.class.php
index f8e5726d344..feb0fd54b15 100644
--- a/htdocs/core/class/extrafields.class.php
+++ b/htdocs/core/class/extrafields.class.php
@@ -699,7 +699,7 @@ class ExtraFields
 					if ($unique) {
 						$sql = "ALTER TABLE ".MAIN_DB_PREFIX.$table." ADD UNIQUE INDEX uk_".$table."_".$attrname." (".$attrname.")";
 					} else {
-						$sql = "ALTER TABLE ".MAIN_DB_PREFIX.$table." DROP INDEX uk_".$table."_".$attrname;
+						$sql = "ALTER TABLE ".MAIN_DB_PREFIX.$table." DROP INDEX IF EXISTS uk_".$table."_".$attrname;
 					}
 					dol_syslog(get_class($this).'::update', LOG_DEBUG);
 					$resql = $this->db->query($sql, 1, 'dml');