diff --git a/account_ebics/models/ebics_config.py b/account_ebics/models/ebics_config.py
index 8c616c7..b315ebd 100644
--- a/account_ebics/models/ebics_config.py
+++ b/account_ebics/models/ebics_config.py
@@ -171,6 +171,7 @@ 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)