diff --git a/sys/arch/xen/include/i82489var.h b/sys/arch/xen/include/i82489var.h
index 5fea526445c1..99a52866d8b1 100644
--- a/sys/arch/xen/include/i82489var.h
+++ b/sys/arch/xen/include/i82489var.h
@@ -1,5 +1,11 @@
-/*	$NetBSD: i82489var.h,v 1.1 2006/09/28 18:53:15 bouyer Exp $	*/
+/*	$NetBSD: i82489var.h,v 1.2 2010/11/14 13:40:31 bouyer Exp $	*/
 
 #include <x86/i82489var.h>
+
+/*
+ * Xen doesn't give acces to the lapic. In addition, the lapic number provided
+ * by the dom0 to Xen when setting up iopics is ignored, the hypervisor will
+ * decide itself to which physical CPU the interrupt should be routed to.
+ */
 #undef lapic_cpu_number
 #define lapic_cpu_number() (0)