diff --git a/accountant/api/models/accounts.py b/accountant/api/models/accounts.py
index d5dfb0e..ee01ff0 100644
--- a/accountant/api/models/accounts.py
+++ b/accountant/api/models/accounts.py
@@ -111,6 +111,6 @@ class Account(db.Model):
 
     @validates('authorized_overdraft')
     def validate_authorized_overdraft(self, key, authorized_overdraft):
-        assert authorized_overdraft > 0
+        assert authorized_overdraft <= 0
 
         return authorized_overdraft