diff --git a/modules/purchase_secondary_unit/CHANGELOG b/modules/purchase_secondary_unit/CHANGELOG
index 39eded0be9..6504dfc5c0 100644
--- a/modules/purchase_secondary_unit/CHANGELOG
+++ b/modules/purchase_secondary_unit/CHANGELOG
@@ -1,3 +1,4 @@
+* Fill secondary unit from product supplier
 * Remove support for Python 3.8
 * Add support for Python 3.13
 
diff --git a/modules/purchase_secondary_unit/purchase.py b/modules/purchase_secondary_unit/purchase.py
index a45c1081ef..de14e5fe86 100644
--- a/modules/purchase_secondary_unit/purchase.py
+++ b/modules/purchase_secondary_unit/purchase.py
@@ -143,15 +143,19 @@ class Line(metaclass=PoolMeta):
     def set_secondary(cls, lines, name, value):
         pass
 
-    @fields.depends('secondary_unit',
+    @fields.depends(
+        'secondary_unit', 'product',
         methods=['on_change_with_secondary_quantity', '_secondary_record'])
     def on_change_product(self):
         super().on_change_product()
         secondary_record = self._secondary_record()
-        if secondary_record and self.secondary_unit:
-            if (self.secondary_unit.category
-                    != secondary_record.purchase_secondary_uom.category):
-                self.secondary_unit = None
+        if secondary_record:
+            secondary_uom = secondary_record.purchase_secondary_uom
+            if self.secondary_unit and secondary_uom:
+                if self.secondary_unit.category != secondary_uom.category:
+                    self.secondary_unit = None
+            if not self.secondary_unit and secondary_record != self.product:
+                self.secondary_unit = secondary_uom
 
         if secondary_record:
             self.secondary_uom_factor = (
diff --git a/modules/purchase_secondary_unit/tests/scenario_purchase_secondary_unit.rst b/modules/purchase_secondary_unit/tests/scenario_purchase_secondary_unit.rst
index 3a85f5e428..5cd13bf6c7 100644
--- a/modules/purchase_secondary_unit/tests/scenario_purchase_secondary_unit.rst
+++ b/modules/purchase_secondary_unit/tests/scenario_purchase_secondary_unit.rst
@@ -85,9 +85,10 @@ Purchase product::
 
 Check secondary unit::
 
-    >>> line.product_supplier = product_supplier
-    >>> line.quantity = 10
-
+    >>> assertEqual(line.secondary_unit, gr)
+    >>> line.secondary_quantity
+    2000.0
+    >>> line.secondary_quantity = None
     >>> line.secondary_unit = kg
     >>> line.secondary_quantity
     2.0