diff --git a/modules/purchase/purchase.py b/modules/purchase/purchase.py
index c1c6c59b4f..8652a7b576 100644
--- a/modules/purchase/purchase.py
+++ b/modules/purchase/purchase.py
@@ -1773,9 +1773,12 @@ 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 3f7f5b675d..6ef9f88b9a 100644
--- a/modules/sale/sale.py
+++ b/modules/sale/sale.py
@@ -1803,9 +1803,12 @@ 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):