diff --git a/config.sample.yaml b/config.sample.yaml
index 144ca2004a5..e18443dd416 100644
--- a/config.sample.yaml
+++ b/config.sample.yaml
@@ -20,7 +20,7 @@ bootstrap_node_inventory: []
     #   address: ""         # (REQUIRED) IP address of the node
     #   controller: true    # (REQUIRED) Set to true if this is a controller node
     #   disk: ""            # (REQUIRED) Device path or serial number of the disk for this node (talosctl disks -n <ip> --insecure)
-    #   mac_addr: ""        # (REQUIRED) MAC address of the NIC for this node (talosctl get links -n <ip> --insecure)
+    #   mac_addr: ""        # (REQUIRED) MAC address of the NIC for this node, must be lowercase (talosctl get links -n <ip> --insecure)
     #   schematic_id: ""    # (OPTIONAL) Override the 'bootstrap_schematic_id' with a node specific schematic ID from https://factory.talos.dev/
     #   mtu: ""             # (OPTIONAL) MTU for the NIC. DEFAULT: 1500
     #   manifests:          # (OPTIONAL) Additional manifests to include after MachineConfig