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
diff --git a/tempest/config.py b/tempest/config.py
index 4ee4669..9ef6c53 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -325,7 +325,8 @@
     cfg.BoolOpt('block_migrate_cinder_iscsi',
                 default=False,
                 help="Does the test environment block migration support "
-                     "cinder iSCSI volumes"),
+                "cinder iSCSI volumes. Note, libvirt doesn't support this, "
+                "see https://bugs.launchpad.net/nova/+bug/1398999"),
     cfg.BoolOpt('vnc_console',
                 default=False,
                 help='Enable VNC console. This configuration value should '