diff --git a/trytond/osv/orm.py b/trytond/osv/orm.py
index 987b28d893..8181ce3961 100644
--- a/trytond/osv/orm.py
+++ b/trytond/osv/orm.py
@@ -1261,10 +1261,11 @@ class ORM(object):
         self.pool.get('ir.model.access').check(cursor, user, self._name,
                 'unlink')
 
-        cursor.execute("SELECT id FROM wkf_instance "\
-                       "WHERE res_id IN ("+",".join(["%s" for i in ids])+") "\
-                       "AND res_type = %s AND state != 'complete'",
-                       (ids+[self._name]))
+        cursor.execute(
+            "SELECT id FROM wkf_instance "\
+                "WHERE res_id IN (" + ",".join(["%s" for i in ids]) + ") "\
+                "AND res_type = %s AND state != 'complete'",
+            (ids+[self._name]))
         if cursor.rowcount != 0:
             raise ExceptORM(
                 'UserError','You cannot delete a record with a running workflow.')