diff --git a/libervia/backend/tools/common/async_process.py b/libervia/backend/tools/common/async_process.py
index f30d2e13..80e0ae31 100644
--- a/libervia/backend/tools/common/async_process.py
+++ b/libervia/backend/tools/common/async_process.py
@@ -1,8 +1,8 @@
 #!/usr/bin/env python3
 
 
-# SAT: a jabber client
-# Copyright (C) 2009-2021 Jérôme Poisson (goffi@goffi.org)
+# Libervia XMPP client
+# Copyright (C) 2009-2026 Jérôme Poisson (goffi@goffi.org)
 
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU Affero General Public License as published by
@@ -34,12 +34,12 @@ log = getLogger(__name__)
 class CommandProtocol(protocol.ProcessProtocol):
     """handle an external command"""
 
-    # name of the command (unicode)
-    name = None
-    # full path to the command (bytes)
-    command = None
-    # True to activate logging of command outputs (bool)
-    log = False
+    # name of the command
+    name: str|None = None
+    # full path to the command
+    command: bytes|None = None
+    # True to activate logging of command outputs
+    log: bool = False
 
     def __init__(self, deferred, stdin=None):
         """
@@ -130,7 +130,8 @@ class CommandProtocol(protocol.ProcessProtocol):
         """
         stdin = kwargs.pop("stdin", None)
         if stdin is not None:
-            stdin = stdin.encode("utf-8")
+            if isinstance(stdin, str):
+                stdin = stdin.encode()
         verbose = kwargs.pop("verbose", False)
         args = list(args)
         d = defer.Deferred()