diff --git a/hosts/helios/README.md b/hosts/helios/README.md
index a832a1c..2ca4e3c 100644
--- a/hosts/helios/README.md
+++ b/hosts/helios/README.md
@@ -13,6 +13,9 @@ Device | Partitions _(filesystem, usage)_
 --- | ---
 SanDisk Ultra II | `/dev/sda1` (ext2, NixOS Boot) <br> `/dev/sda2` (ZFS, NixOS Root)
 
+> Note: The BIOS firmware on this machine only supports booting from disks with
+> an MBR partition table.
+
 #### ZFS pool layout
 ```
 rpool/