diff --git a/tryton/tryton/gui/window/view_form/model/field.py b/tryton/tryton/gui/window/view_form/model/field.py
index 649b302dc9..332b6c400c 100644
--- a/tryton/tryton/gui/window/view_form/model/field.py
+++ b/tryton/tryton/gui/window/view_form/model/field.py
@@ -872,7 +872,7 @@ class O2MField(Field):
                 record2 = group.get(vals['id'])
                 if record2 is not None:
                     to_set = {
-                        k: v for k, v in vals.items
+                        k: v for k, v in vals.items()
                         if k not in vals_to_set}
                     record2.set_on_change(to_set)