diff --git a/migration/vyos-mode-delta.py b/migration/vyos-mode-delta.py
index e81434f..1b646d7 100755
--- a/migration/vyos-mode-delta.py
+++ b/migration/vyos-mode-delta.py
@@ -85,6 +85,14 @@ def build_delta(inv: dict, priority: int, wan_user: str) -> list[str]:
         "# Vodafone line, PPPoE over the trunked WAN VLAN. This is the one",
         "# part that cannot be tested before cutover: the line permits a",
         "# single session and the USG holds it until it is unplugged.",
+        "#",
+        "# The WAN vif must be created first. Neither firewall has vif 51 today",
+        "# (only 2, 3, 9, 10 and 200 exist), and pppoe source-interface refers to",
+        "# an interface that has to already be configured -- without this the",
+        "# commit fails and takes the whole switch with it. No address on it:",
+        "# PPPoE rides the VLAN, it does not need L3 of its own.",
+        f"set interfaces bonding bond0 vif {WAN_VIF.split('.')[1]} description 'WAN (Vodafone, PPPoE)'",
+        "",
         f"set interfaces pppoe {WAN_IF} source-interface {WAN_VIF}",
         f"set interfaces pppoe {WAN_IF} authentication username '{wan_user}'",
         f"set interfaces pppoe {WAN_IF} authentication password '{PLACEHOLDER}'",