diff --git a/addons/stock/models/stock_scrap.py b/addons/stock/models/stock_scrap.py
index 4bf89e24a68..2e7d6eb021e 100644
--- a/addons/stock/models/stock_scrap.py
+++ b/addons/stock/models/stock_scrap.py
@@ -66,6 +66,8 @@ class StockScrap(models.Model):
     @api.onchange('product_id')
     def _onchange_product_id(self):
         if self.product_id:
+            if self.tracking == 'serial':
+                self.scrap_qty = 1
             self.product_uom_id = self.product_id.uom_id.id
             # Check if we can get a more precise location instead of
             # the default location (a location corresponding to where the
diff --git a/addons/stock/views/stock_scrap_views.xml b/addons/stock/views/stock_scrap_views.xml
index 311149dc43c..6c88a0988ea 100644
--- a/addons/stock/views/stock_scrap_views.xml
+++ b/addons/stock/views/stock_scrap_views.xml
@@ -157,7 +157,8 @@
                             <field name="product_id" options="{'no_create': True}" domain="[('id', 'in', context.get('product_ids', []))]"/>
                             <label for="scrap_qty"/>
                             <div class="o_row">
-                                <field name="scrap_qty"/>
+                                <field name="scrap_qty"
+                                    attrs="{'readonly': [('tracking', '=', 'serial')]}"/>
                                 <field name="product_uom_category_id" invisible="1"/>
                                 <field name="product_uom_id" groups="uom.group_uom"/>
                             </div>
@@ -165,7 +166,9 @@
                         <group>
                             <field name="picking_id" invisible="1"/>
                             <field name="tracking" invisible="1"/>
-                            <field name="lot_id" attrs="{'invisible': ['|',('product_id', '=', False),('tracking', '=', 'none')], 'required': [('tracking', '!=', 'none')]}" groups="stock.group_production_lot"/>
+                            <field name="lot_id" groups="stock.group_production_lot"
+                                context="{'default_company_id': company_id, 'default_product_id': product_id}"
+                                attrs="{'invisible': ['|',('product_id', '=', False),('tracking', '=', 'none')], 'required': [('tracking', '!=', 'none')]}"/>
                             <field name="package_id" groups="stock.group_tracking_lot"/>
                             <field name="owner_id" groups="stock.group_tracking_owner"/>
                             <field name="company_id" invisible="1"/>