diff --git a/tests/cmc-upgrade-kernel-test.md b/tests/cmc-upgrade-kernel-test.md
index c7c3af4..e67ee17 100644
--- a/tests/cmc-upgrade-kernel-test.md
+++ b/tests/cmc-upgrade-kernel-test.md
@@ -106,7 +106,7 @@ Validate CMC behavior across staged kernel upgrades on a cloned VM, including re
 26. SSH to the new live clone IP and verify the DHCP state.
 27. If the clone still reports the previous static IP, fix static config cleanup and repeat reboot/verify.
 28. Continue all remaining steps using the live DHCP IP from vCenter and credentials from `/home/aw/code/cds/.env.credentials.local`.
-29. Before the first CMC install, wipe the 10GB source disk so it has no filesystem, partition table, or other residual content. This disk prep is one-time only and must not be repeated in later stages of the test.
+29. Before the first CMC install, wipe the 10GB source disk with `dd if=/dev/zero of=/dev/sdb bs=1M count=32 status=progress conv=fsync`, then verify that no filesystem or partition signatures remain (`wipefs -n /dev/sdb`, `blkid /dev/sdb`, `file -s /dev/sdb`, `lsblk -f /dev/sdb`). This disk prep is one-time only and must not be repeated in later stages of the test.
 30. Using `cirrusdata` (`gcstage`, project `skidamarink`), reinstall CMC on clone, always adding `-no-prebuilt-mtdi-nexus`.
 31. Create local migration from 10GB source disk to 11GB destination disk using `cirrusdata`.
 32. If migration session creation fails (including API/service errors such as 5xx), hard stop as blocker-fail.