diff --git a/htdocs/core/modules/import/import_xlsx.modules.php b/htdocs/core/modules/import/import_xlsx.modules.php
index 18cf7c767ac..80436abacd5 100644
--- a/htdocs/core/modules/import/import_xlsx.modules.php
+++ b/htdocs/core/modules/import/import_xlsx.modules.php
@@ -651,6 +651,9 @@ class ImportXlsx extends ModeleImports
 								}
 							} else {
 								// We have a last INSERT ID. Check if we have a row referencing this foreign key.
+								// This is required when updating table with some extrafields. When inserting a record in parent table, we can make 
+								// a direct insert into subtable extrafields, but when me wake an update, the insertid is defined and the child record 
+								// may already exists. So we rescan the extrafield table to be know if record exists or not for the rowid.
 								$sqlSelect = 'SELECT rowid FROM '.$tablename;
 
 								if(empty($keyfield)) $keyfield = 'rowid';