diff --git a/issue12823.diff b/issue12823.diff
new file mode 100644
index 0000000..97d5508
--- /dev/null
+++ b/issue12823.diff
@@ -0,0 +1,36 @@
+diff --git a/tryton/modules/account/move.py b/tryton/modules/account/move.py
+index b827237af4..ddbca0ae19 100644
+--- a/tryton/modules/account/move.py
++++ b/tryton/modules/account/move.py
+@@ -1098,7 +1098,7 @@ class Line(MoveLineMixin, ModelSQL, ModelView):
+     def on_change_move(self):
+         if self.move:
+             if not self.debit and not self.credit:
+-                total = sum(l.debit - l.credit
++                total = sum((l.debit or 0) - (l.credit or 0)
+                     for l in getattr(self.move, 'lines', []))
+                 self.debit = -total if total < 0 else Decimal(0)
+                 self.credit = total if total > 0 else Decimal(0)
+@@ -1169,7 +1169,8 @@ class Line(MoveLineMixin, ModelSQL, ModelView):
+         'Set correct sign to amount_second_currency'
+         if self.amount_second_currency:
+             self.amount_second_currency = \
+-                self.amount_second_currency.copy_sign(self.debit - self.credit)
++                self.amount_second_currency.copy_sign(
++                    (self.debit or 0) - (self.credit or 0))
+
+     @fields.depends('account')
+     def on_change_account(self):
+@@ -2402,9 +2403,11 @@ class ReconcileShow(ModelView):
+         if self.currency:
+             for line in self.lines:
+                 if line.second_currency == self.currency:
+-                    amount += line.amount_second_currency
++                    amount += (
++                        line.amount_second_currency or 0)
+                 elif line.currency == self.currency:
+-                    amount += line.debit - line.credit
++                    amount += (
++                        (line.debit or 0) - (line.credit or 0))
+             amount = self.currency.round(amount)
+         self.write_off_amount = amount
diff --git a/series b/series
index 8e2a78d..7669a03 100644
--- a/series
+++ b/series
@@ -65,3 +65,5 @@ sao_document_field.diff # [sao] fix issue with loading of 'document' fields in s
 issue12799.diff # [sao] Convert negative id value as None when set by the client
 
 issue12547.diff # [stock_lot] Check lot required only when changing move to done
+
+issue12823.diff # [account] Use 0 as fallback for missing debit or credit in on_change functions