diff --git a/node-definitions/opnsense/README.md b/node-definitions/opnsense/README.md
index 9141943..60c11e7 100644
--- a/node-definitions/opnsense/README.md
+++ b/node-definitions/opnsense/README.md
@@ -2,3 +2,4 @@
 
 Here you will find collections of OPNsense node definitions.
 
+**NOTE:** There seems to be an odd ACPI issue that prevents OPNsense from booting within CML when using a single CPU. Setting the CPU count to two resolved the issue. No further details are available.