diff --git a/addons/account/models/account_move.py b/addons/account/models/account_move.py
index bef59e4282e..0f0384b4cb7 100644
--- a/addons/account/models/account_move.py
+++ b/addons/account/models/account_move.py
@@ -2254,7 +2254,7 @@ class AccountMove(models.Model):
         return copied_am
 
     def _sanitize_vals(self, vals):
-        if 'invoice_line_ids' in vals and 'line_ids' in vals:
+        if vals.get('invoice_line_ids') and vals.get('line_ids'):
             # values can sometimes be in only one of the two fields, sometimes in
             # both fields, sometimes one field can be explicitely empty while the other
             # one is not, sometimes not...