diff --git a/etc/tempest.conf.sample b/etc/tempest.conf.sample
index 2e57007..3333cbb 100644
--- a/etc/tempest.conf.sample
+++ b/etc/tempest.conf.sample
@@ -393,7 +393,8 @@
 #block_migration_for_live_migration = false
 
 # Does the test environment block migration support cinder iSCSI
-# volumes (boolean value)
+# volumes. Note, libvirt doesn't support this, see
+# https://bugs.launchpad.net/nova/+bug/1398999 (boolean value)
 #block_migrate_cinder_iscsi = false
 
 # Enable VNC console. This configuration value should be same as