diff --git a/modules/purchase/purchase.py b/modules/purchase/purchase.py
index be4462e1d5..d7eae8784f 100644
--- a/modules/purchase/purchase.py
+++ b/modules/purchase/purchase.py
@@ -1637,9 +1637,12 @@ class Line(sequence_ordered(), ModelSQL, ModelView):
             if invoice_line.type != 'line':
                 continue
             if invoice_line not in skips:
-                quantity += Uom.compute_qty(
-                    invoice_line.unit or self.unit, invoice_line.quantity,
-                    self.unit)
+                if self.unit:
+                    quantity += Uom.compute_qty(
+                        invoice_line.unit or self.unit, invoice_line.quantity,
+                        self.unit)
+                else:
+                    quantity += invoice_line.quantity
         return quantity
 
     def _get_invoice_line_moves(self):
diff --git a/modules/sale/sale.py b/modules/sale/sale.py
index e3750d0997..30d0e5f0db 100644
--- a/modules/sale/sale.py
+++ b/modules/sale/sale.py
@@ -1585,9 +1585,12 @@ class SaleLine(TaxableMixin, sequence_ordered(), ModelSQL, ModelView):
             if invoice_line.type != 'line':
                 continue
             if invoice_line not in skips:
-                quantity += Uom.compute_qty(
-                    invoice_line.unit or self.unit, invoice_line.quantity,
-                    self.unit)
+                if self.unit:
+                    quantity += Uom.compute_qty(
+                        invoice_line.unit or self.unit, invoice_line.quantity,
+                        self.unit)
+                else:
+                    quantity += invoice_line.quantity
         return quantity
 
     def _get_invoice_line_moves(self):