diff --git a/folio.py b/folio.py
index c951465..2d5bf1a 100644
--- a/folio.py
+++ b/folio.py
@@ -457,7 +457,7 @@ class Folio(ModelSQL, ModelView):
         res = []
         amount_nights = 0
         if self.nights_quantity and self.unit_price_w_tax:
-            amount_nights = [self.nights_quantity * self.unit_price_w_tax]
+            amount_nights = self.nights_quantity * self.unit_price_w_tax
         if name == 'total_amount' or (name == 'total_balance' and not self.invoice_line):
             res.append(amount_nights)
         for charge in self.charges: