diff --git a/view/purchase_line_tree.xml b/view/purchase_line_tree.xml
index b29c985350..ae10ef07fd 100644
--- a/view/purchase_line_tree.xml
+++ b/view/purchase_line_tree.xml
@@ -3,7 +3,7 @@
 this repository contains the full copyright notices and license terms. -->
 <data>
     <xpath expr="//field[@name='unit_price']" position="after">
-        <field name="secondary_quantity" symbol="secondary_unit"/>
-        <field name="secondary_unit_price"/>
+        <field name="secondary_quantity" symbol="secondary_unit" optional="1"/>
+        <field name="secondary_unit_price" optional="1"/>
     </xpath>
 </data>