diff --git a/utils/pack_fw.py b/utils/pack_fw.py
index 93f87027e6..9c7f4a8fd6 100644
--- a/utils/pack_fw.py
+++ b/utils/pack_fw.py
@@ -105,6 +105,8 @@ def write_version(ver, *, build_number: int):
         data += getattr(ver, it).to_bytes(1, 'little')
     data += build_number.to_bytes(2, 'little')
     data += ver.prerelease.ljust(5, '\0').encode()
+    if len(data) != 10:
+        raise ValueError('version must be 10 bytes long')
     return data