diff --git a/account_ebics/models/ebics_config.py b/account_ebics/models/ebics_config.py
index 530ed7c..4224b10 100644
--- a/account_ebics/models/ebics_config.py
+++ b/account_ebics/models/ebics_config.py
@@ -232,6 +232,7 @@ class EbicsConfig(models.Model):
                 o_list[-i] = "A"
                 break
             if c == "Z":
+                o_list[-i] = "0"
                 continue
             else:
                 o_list[-i] = chr(ord(c) + 1)