diff --git a/contract_variable_quantity/models/contract_line.py b/contract_variable_quantity/models/contract_line.py
index 4631b329..1ac894f9 100644
--- a/contract_variable_quantity/models/contract_line.py
+++ b/contract_variable_quantity/models/contract_line.py
@@ -47,7 +47,7 @@ class AccountAnalyticInvoiceLine(models.Model):
                     contract_line_qty=qty
                 ).price_unit
         else:
-            if vals.get('quantity') and vals['quantity'] == 0:
+            if 'quantity' in vals and vals['quantity'] == 0:
                 # Skip zero should ignore lines with qty zero even for fixed
                 # qty
                 vals = {}