diff --git a/book.py b/book.py
index 2393bab..76d3464 100644
--- a/book.py
+++ b/book.py
@@ -204,8 +204,11 @@ class Book(SymbolMixin, metaclass=PoolMeta):
     def on_change_with_yield_balance(self, name=None):
         """ calculate yield total
         """
-        return self.diff_amount + self.yield_dividend_total + \
-            self.yield_sales - self.yield_fee_total
+        sum_lst = [self.diff_amount, self.yield_dividend_total, self.yield_sales]
+        sum2 = sum([x for x in sum_lst if x is not None])
+        if self.yield_fee_total is not None:
+            sum2 -= self.yield_fee_total
+        return sum2
 
     @classmethod
     def get_yield_data_sql(cls, date_from=None, date_to=None):
diff --git a/tests/test_yield.py b/tests/test_yield.py
index d1ebb9f..11f8773 100644
--- a/tests/test_yield.py
+++ b/tests/test_yield.py
@@ -157,6 +157,12 @@ class YieldTestCase(ModuleTestCase):
         self.assertEqual(lines[0].trade_fee, Decimal('4.0'))
         self.assertEqual(book_asset.rec_name, 'Depot | 19.50 usd | Open | 3.0000 u')
 
+        self.assertEqual(book_asset.yield_dividend_total, Decimal('23.5'))
+        self.assertEqual(book_asset.yield_fee_total, Decimal('4.0'))
+        self.assertEqual(book_asset.yield_sales, Decimal('0.0'))
+        self.assertEqual(book_asset.diff_amount, Decimal('-19.5'))
+        self.assertEqual(book_asset.yield_balance, Decimal('0.0'))
+
     @with_transaction()
     def test_yield_fee_transfer_from_splitbooking_cash_out(self):
         """ check out-booking, transfer from cash --> asset,