diff --git a/zigpy_cli/ota.py b/zigpy_cli/ota.py
index c806c13..8b2623f 100644
--- a/zigpy_cli/ota.py
+++ b/zigpy_cli/ota.py
@@ -126,6 +126,7 @@ def generate_index(ctx, ota_url_root, output, files):
         metadata = {
             "binary_url": url,
             "file_version": image.header.file_version,
+            "file_size": len(contents),
             "image_type": image.header.image_type,
             "manufacturer_id": image.header.manufacturer_id,
             "changelog": "",