diff --git a/aiven/client/client.py b/aiven/client/client.py
index ac0e6e7..fa89278 100644
--- a/aiven/client/client.py
+++ b/aiven/client/client.py
@@ -1639,7 +1639,7 @@ def get_account_authentication_methods(self, account_id: str) -> Sequence[dict[s
     def create_project(
         self,
         project: str,
-        account_id: str | None,
+        account_id: str | None = None,
         billing_group_id: str | None = None,
         cloud: str | None = None,
         copy_from_project: str | None = None,