diff --git a/accounting/storage/__init__.py b/accounting/storage/__init__.py
index bbaa16d..4985a07 100644
--- a/accounting/storage/__init__.py
+++ b/accounting/storage/__init__.py
@@ -26,6 +26,10 @@ class Storage():
     def get_accounts(self, *args, **kw):
         raise NotImplementedError
 
+    @abstractmethod
+    def add_transaction(self, transaction):
+        raise NotImplementedError
+
     @abstractmethod
     def update_transaction(self, transaction):
         raise NotImplementedError