diff --git a/mis_builder/models/accounting_none.py b/mis_builder/models/accounting_none.py
index 5249e540..de65ac1f 100644
--- a/mis_builder/models/accounting_none.py
+++ b/mis_builder/models/accounting_none.py
@@ -17,6 +17,8 @@ the same as zero.
 1
 >>> AccountingNone + None
 AccountingNone
+>>> None + AccountingNone
+AccountingNone
 >>> +AccountingNone
 AccountingNone
 >>> -AccountingNone
@@ -31,6 +33,8 @@ AccountingNone
 AccountingNone
 >>> AccountingNone - None
 AccountingNone
+>>> None - AccountingNone
+AccountingNone
 >>> AccountingNone / 2
 0.0
 >>> 2 / AccountingNone