diff --git a/docs/man/xl.pod.1 b/docs/man/xl.pod.1
index a765a11617..7620a2bcb0 100644
--- a/docs/man/xl.pod.1
+++ b/docs/man/xl.pod.1
@@ -614,6 +614,9 @@ Prints the current uptime of the domains running.
 =item B<pci-list-assignable-devices>
 
 List all the assignable PCI devices.
+These are devices in the system which are configured to be
+available for passthrough and are bound to a suitable PCI
+backend driver in domain 0 rather than a real driver.
 
 =back