diff --git a/CHANGELOG b/CHANGELOG
index d3f7870224..069056b0c5 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,5 @@
+* Support amend line without product
+
 Version 5.8.0 - 2020-11-02
 * Bug fixes (see mercurial logs for details)
 * Remove support for Python 3.5
diff --git a/sale.py b/sale.py
index 042ff76bda..0448d0ac26 100644
--- a/sale.py
+++ b/sale.py
@@ -4,7 +4,7 @@
 from trytond.i18n import gettext
 from trytond.model import ModelSQL, ModelView, Workflow, fields
 from trytond.pool import Pool, PoolMeta
-from trytond.pyson import Eval, If
+from trytond.pyson import Eval, If, Bool
 
 from trytond.modules.product import price_digits
 
@@ -267,12 +267,13 @@ class AmendmentLine(ModelSQL, ModelView):
             If(Eval('state') == 'draft',
                 ('salable', '=', True),
                 ()),
-            ('default_uom_category', '=', Eval('product_uom_category')),
+            If(Eval('product_uom_category'),
+                ('default_uom_category', '=', Eval('product_uom_category')),
+                ()),
             ],
         states={
             'readonly': Eval('state') != 'draft',
             'invisible': Eval('action') != 'line',
-            'required': Eval('action') == 'line',
             },
         depends=['action', 'state', 'product_uom_category'])
     quantity = fields.Float(
@@ -287,14 +288,16 @@ class AmendmentLine(ModelSQL, ModelView):
     unit = fields.Many2One(
         'product.uom', "Unit", ondelete='RESTRICT',
         domain=[
-            ('category', '=', Eval('product_uom_category')),
+            If(Eval('product_uom_category'),
+                ('category', '=', Eval('product_uom_category')),
+                ()),
             ],
         states={
             'readonly': Eval('state') != 'draft',
             'invisible': Eval('action') != 'line',
-            'required': Eval('action') == 'line',
+            'required': Bool(Eval('product')),
             },
-        depends=['state', 'product_uom_category', 'action'])
+        depends=['state', 'product_uom_category', 'action', 'product'])
     unit_price = fields.Numeric(
         "Unit Price", digits=price_digits,
         states={
@@ -406,7 +409,10 @@ class AmendmentLine(ModelSQL, ModelView):
     @fields.depends('line')
     def on_change_with_product_uom_category(self, name=None):
         if self.line:
-            return self.line.product_uom_category.id
+            if self.line.product_uom_category:
+                return self.line.product_uom_category.id
+            elif self.line.unit:
+                return self.line.unit.category.id
 
     def apply(self, sale):
         assert self.sale == sale
@@ -420,7 +426,8 @@ class AmendmentLine(ModelSQL, ModelView):
 
     def _apply_taxes(self, sale, sale_line):
         for line in sale.lines:
-            line.taxes = line.compute_taxes(sale.party)
+            if line.product:
+                line.taxes = line.compute_taxes(sale.party)
 
     def _apply_payment_term(self, sale, sale_line):
         sale.payment_term = self.payment_term
diff --git a/tests/scenario_sale_amendment.rst b/tests/scenario_sale_amendment.rst
index 4777b1c368..f91358962a 100644
--- a/tests/scenario_sale_amendment.rst
+++ b/tests/scenario_sale_amendment.rst
@@ -78,6 +78,9 @@ Sale first product::
     >>> sale_line = sale.lines.new()
     >>> sale_line.product = product1
     >>> sale_line.quantity = 5.0
+    >>> sale_line = sale.lines.new()
+    >>> sale_line.quantity = 1
+    >>> sale_line.unit_price = Decimal('5.0000')
     >>> sale.click('quote')
     >>> sale.click('confirm')
     >>> sale.state
@@ -85,7 +88,7 @@ Sale first product::
     >>> sale.revision
     0
     >>> sale.total_amount
-    Decimal('50.00')
+    Decimal('55.00')
     >>> len(sale.shipments), len(sale.invoices)
     (1, 1)
 
@@ -107,7 +110,7 @@ Add an amendment::
     True
     >>> line = amendment.lines.new()
     >>> line.action = 'line'
-    >>> line.line, = sale.lines
+    >>> line.line = sale.lines[0]
     >>> line.product == product1
     True
     >>> line.product = product2
@@ -117,6 +120,11 @@ Add an amendment::
     >>> line.unit_price
     Decimal('10.0000')
     >>> line.unit_price = Decimal('9.0000')
+    >>> line = amendment.lines.new()
+    >>> line.action = 'line'
+    >>> line.line = sale.lines[1]
+    >>> line.product
+    >>> line.quantity = 2
     >>> amendment.save()
 
 Validate amendment::
@@ -127,15 +135,18 @@ Validate amendment::
     1
     >>> sale.party == customer2
     True
-    >>> line, = sale.lines
+    >>> line = sale.lines[0]
     >>> line.product == product2
     True
     >>> line.quantity
     4.0
     >>> line.unit_price
     Decimal('9.0000')
+    >>> line = sale.lines[1]
+    >>> line.quantity
+    2.0
     >>> sale.total_amount
-    Decimal('36.00')
+    Decimal('46.00')
 
     >>> shipment, = sale.shipments
     >>> move, = shipment.outgoing_moves
@@ -145,10 +156,16 @@ Validate amendment::
     4.0
 
     >>> invoice, = sale.invoices
-    >>> line, = invoice.lines
+    >>> line = invoice.lines[0]
     >>> line.product == product2
     True
     >>> line.quantity
     4.0
     >>> line.unit_price
     Decimal('9.0000')
+    >>> line = invoice.lines[1]
+    >>> line.product
+    >>> line.quantity
+    2.0
+    >>> line.unit_price
+    Decimal('5.0000')