diff --git a/api/controllers/files/image_preview.py b/api/controllers/files/image_preview.py
index 6f39908b6e..5adfe16a79 100644
--- a/api/controllers/files/image_preview.py
+++ b/api/controllers/files/image_preview.py
@@ -75,6 +75,7 @@ class FilePreviewApi(Resource):
         if args["as_attachment"]:
             encoded_filename = quote(upload_file.name)
             response.headers["Content-Disposition"] = f"attachment; filename*=UTF-8''{encoded_filename}"
+        response.headers["Content-Type"] = "application/octet-stream"
 
         return response