diff --git a/trytond/backend/postgresql/database.py b/trytond/backend/postgresql/database.py
index 137458bf55..6e098c3d23 100644
--- a/trytond/backend/postgresql/database.py
+++ b/trytond/backend/postgresql/database.py
@@ -282,7 +282,7 @@ class Cursor(CursorInterface):
                 res = self.cursor.execute(sql)
         except:
             logger = logging.getLogger('sql')
-            logger.error('Wrong SQL: ' + self.cursor.query)
+            logger.error('Wrong SQL: ' + (self.cursor.query or ''))
             raise
         if self.sql_log:
             res_from = RE_FROM.match(sql.lower())