diff --git a/addons/sale/sale.py b/addons/sale/sale.py
index 2925d35c545..6258d63e8b8 100644
--- a/addons/sale/sale.py
+++ b/addons/sale/sale.py
@@ -728,7 +728,7 @@ class SaleOrderLine(models.Model):
 
         vals = {}
         domain = {'product_uom': [('category_id', '=', self.product_id.uom_id.category_id.id)]}
-        if not (self.product_uom and (self.product_id.uom_id.category_id.id == self.product_uom.category_id.id)):
+        if not self.product_uom or (self.product_id.uom_id.category_id.id != self.product_uom.category_id.id):
             vals['product_uom'] = self.product_id.uom_id
 
         product = self.product_id.with_context(
diff --git a/addons/sale_stock/sale_stock.py b/addons/sale_stock/sale_stock.py
index 9c7fe4bea02..9f04e4b5833 100644
--- a/addons/sale_stock/sale_stock.py
+++ b/addons/sale_stock/sale_stock.py
@@ -130,7 +130,13 @@ class SaleOrderLine(models.Model):
             return self._check_package()
         return {}
 
-    @api.onchange('product_id', 'product_uom_qty', 'product_uom', 'route_id')
+    @api.onchange('product_id')
+    def _onchange_product_id_uom_check_availability(self):
+        if not self.product_uom or (self.product_id.uom_id.category_id.id != self.product_uom.category_id.id):
+            self.product_uom = self.product_id.uom_id
+        self._onchange_product_id_check_availability()
+
+    @api.onchange('product_uom_qty', 'product_uom', 'route_id')
     def _onchange_product_id_check_availability(self):
         if not self.product_id or not self.product_uom_qty or not self.product_uom:
             self.product_packaging = False