diff --git a/storage_s3/indico_storage_s3/storage.py b/storage_s3/indico_storage_s3/storage.py
index 7283afd..2f83e43 100644
--- a/storage_s3/indico_storage_s3/storage.py
+++ b/storage_s3/indico_storage_s3/storage.py
@@ -26,7 +26,9 @@ from indico.core.config import config
 from indico.core.storage import Storage, StorageError
 from indico.core.storage.backend import ReadOnlyStorageMixin, StorageReadOnlyError
 from indico.util.fs import get_file_checksum
-from indico.web.flask.util import make_content_disposition_args, send_file
+from indico.web.flask.util import send_file
+
+from indico_storage_s3.util import make_content_disposition_args
 
 
 s3_session_cache = threading.local()
diff --git a/storage_s3/indico_storage_s3/util.py b/storage_s3/indico_storage_s3/util.py
new file mode 100644
index 0000000..ce3f5c8
--- /dev/null
+++ b/storage_s3/indico_storage_s3/util.py
@@ -0,0 +1,22 @@
+# This file is part of the Indico plugins.
+# Copyright (C) 2002 - 2021 CERN
+#
+# The Indico plugins are free software; you can redistribute
+# them and/or modify them under the terms of the MIT License;
+# see the LICENSE file for more details.
+
+import unicodedata
+
+from werkzeug.urls import url_quote
+
+
+def make_content_disposition_args(attachment_filename):
+    try:
+        attachment_filename = attachment_filename.encode('ascii')
+    except UnicodeEncodeError:
+        return {
+            'filename': unicodedata.normalize('NFKD', attachment_filename).encode('ascii', 'ignore'),
+            'filename*': "UTF-8''%s" % url_quote(attachment_filename, safe=b''),
+        }
+    else:
+        return {'filename': attachment_filename}