diff --git a/backend/api/documents.py b/backend/api/documents.py
index 97ed572..907c648 100644
--- a/backend/api/documents.py
+++ b/backend/api/documents.py
@@ -21,6 +21,7 @@ to all handlers. The doc.user_id=None guard in /confirm is a Wave 2 placeholder.
 """
 from __future__ import annotations
 
+import urllib.parse
 import uuid
 from pathlib import Path
 from typing import Optional
@@ -786,9 +787,10 @@ async def stream_document_content(
         ) from exc
     file_size = len(file_bytes)
 
+    safe_name = urllib.parse.quote(doc.filename, safe='')
     headers = {
         "content-type": doc.content_type,
-        "content-disposition": f'inline; filename="{doc.filename}"',
+        "content-disposition": f"inline; filename*=UTF-8''{safe_name}",
         "accept-ranges": "bytes",
         "content-length": str(file_size),
     }