diff --git a/backend/auth/router.py b/backend/auth/router.py
index 77220cf..ff78aba 100644
--- a/backend/auth/router.py
+++ b/backend/auth/router.py
@@ -7,6 +7,7 @@ import binascii
 import logging
 import os
 import re
+from datetime import UTC
 
 from fastapi import APIRouter, Body, Depends, HTTPException, Request, Response
 from pydantic import BaseModel, validator
@@ -696,7 +697,7 @@ async def mfa_webauthn_register(
 
     Returns recovery codes when MFA is newly enabled (they were never issued).
     """
-    from datetime import datetime, timezone
+    from datetime import datetime
 
     from .user_store import get_user, update_user
     from .webauthn_mfa import complete_registration, resolve_relying_party
@@ -716,7 +717,7 @@ async def mfa_webauthn_register(
         logger.warning(f"WebAuthn registration failed for {current_user['username']}: {e}")
         raise HTTPException(400, "Validation du credential WebAuthn échouée")
 
-    record["registered_at"] = datetime.now(timezone.utc).isoformat()
+    record["registered_at"] = datetime.now(UTC).isoformat()
     creds = list(user.get("webauthn_credentials", []))
     creds = [c for c in creds if c.get("credential_id") != record["credential_id"]]
     creds.append(record)