diff --git a/app.py b/app.py
index bfb5a18..2f6cd07 100644
--- a/app.py
+++ b/app.py
@@ -10,6 +10,7 @@ import json
 import logging
 import os
 import re
+import tempfile
 import threading
 import time
 import uuid
@@ -458,7 +459,7 @@ def api_avatar():
 
     # Build a safe cache filename from the username (alphanumeric + - _ .)
     safe_name = re.sub(r'[^a-zA-Z0-9._-]', '_', username)
-    cache_dir = ldap_cfg.get('cache_dir', '/tmp/gandalf_avatars')
+    cache_dir = ldap_cfg.get('cache_dir', os.path.join(tempfile.gettempdir(), 'gandalf_avatars'))
     os.makedirs(cache_dir, exist_ok=True)
     cache_file = os.path.join(cache_dir, f'user_{safe_name}.jpg')
     sentinel    = os.path.join(cache_dir, f'user_{safe_name}.none')