diff --git a/modules/purchase_trade/purchase.py b/modules/purchase_trade/purchase.py
index 1c55e16..49b3caa 100755
--- a/modules/purchase_trade/purchase.py
+++ b/modules/purchase_trade/purchase.py
@@ -1225,9 +1225,14 @@ class Line(metaclass=PoolMeta):
             return None
         unit_factor = Decimal(1)
         if self.linked_unit:
+            source_unit = getattr(self, 'unit', None)
+            if not source_unit and self.product:
+                source_unit = self.product.purchase_uom or self.product.default_uom
+            if not source_unit:
+                return factor
             Uom = Pool().get('product.uom')
             unit_factor = Decimal(str(
-                Uom.compute_qty(self.unit, float(1), self.linked_unit) or 0))
+                Uom.compute_qty(source_unit, float(1), self.linked_unit) or 0))
         return factor * unit_factor
 
     def _linked_to_line_price(self, price):
@@ -1304,7 +1309,8 @@ class Line(metaclass=PoolMeta):
         return self.get_price()
 
     @fields.depends(
-        'type', 'quantity', 'unit_price', 'purchase', '_parent_purchase.currency',
+        'type', 'quantity', 'unit_price', 'unit', 'product',
+        'purchase', '_parent_purchase.currency',
         'premium', 'enable_linked_currency', 'linked_currency', 'linked_unit')
     def on_change_with_amount(self):
         if (self.type == 'line'
@@ -1318,7 +1324,10 @@ class Line(metaclass=PoolMeta):
             return amount
         return Decimal(0)
 
-    @fields.depends(methods=['on_change_with_unit_price', 'on_change_with_amount'])
+    @fields.depends(
+        'unit', 'product', 'price_type', 'enable_linked_currency',
+        'linked_currency', 'linked_unit', 'linked_price', 'premium',
+        methods=['on_change_with_unit_price', 'on_change_with_amount'])
     def _recompute_trade_price_fields(self):
         self.unit_price = self.on_change_with_unit_price()
         self.amount = self.on_change_with_amount()
diff --git a/modules/purchase_trade/sale.py b/modules/purchase_trade/sale.py
index 51cb4b2..090b1c6 100755
--- a/modules/purchase_trade/sale.py
+++ b/modules/purchase_trade/sale.py
@@ -778,9 +778,14 @@ class SaleLine(metaclass=PoolMeta):
             return None
         unit_factor = Decimal(1)
         if self.linked_unit:
+            source_unit = getattr(self, 'unit', None)
+            if not source_unit and self.product:
+                source_unit = self.product.sale_uom
+            if not source_unit:
+                return factor
             Uom = Pool().get('product.uom')
             unit_factor = Decimal(str(
-                Uom.compute_qty(self.unit, float(1), self.linked_unit) or 0))
+                Uom.compute_qty(source_unit, float(1), self.linked_unit) or 0))
         return factor * unit_factor
 
     def _linked_to_line_price(self, price):
@@ -852,7 +857,8 @@ class SaleLine(metaclass=PoolMeta):
         return self.get_price()
 
     @fields.depends(
-        'type', 'quantity', 'unit_price', 'sale', '_parent_sale.currency',
+        'type', 'quantity', 'unit_price', 'unit', 'product',
+        'sale', '_parent_sale.currency',
         'premium', 'enable_linked_currency', 'linked_currency', 'linked_unit')
     def on_change_with_amount(self):
         if self.type == 'line':
@@ -864,7 +870,10 @@ class SaleLine(metaclass=PoolMeta):
             return amount
         return Decimal(0)
 
-    @fields.depends(methods=['on_change_with_unit_price', 'on_change_with_amount'])
+    @fields.depends(
+        'unit', 'product', 'price_type', 'enable_linked_currency',
+        'linked_currency', 'linked_unit', 'linked_price', 'premium',
+        methods=['on_change_with_unit_price', 'on_change_with_amount'])
     def _recompute_trade_price_fields(self):
         self.unit_price = self.on_change_with_unit_price()
         self.amount = self.on_change_with_amount()