diff --git a/classquiz/storage/s3_storage.py b/classquiz/storage/s3_storage.py
index 458b6fc..913d80e 100644
--- a/classquiz/storage/s3_storage.py
+++ b/classquiz/storage/s3_storage.py
@@ -5,6 +5,7 @@
 
 import hashlib
 import hmac
+import sys
 from datetime import datetime, timedelta
 from typing import Tuple, BinaryIO, Generator
 
@@ -110,6 +111,7 @@ class S3Storage:
     # skipcq: PYL-W0613
     async def upload(self, file: BinaryIO, file_name: str, mime_type: str | None = "application/octet-stream") -> None:
         headers, url = self._generate_aws_signature_v4(method="PUT", path=f"/{file_name}")
+        headers["Content-Length"] = sys.getsizeof(file)
         async with ClientSession() as session, session.put(url, headers=headers, data=file) as resp:
             if resp.status == 200:
                 return None