diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
index 5dc5872e38..c31afc734f 100644
--- a/xen/arch/x86/dom0_build.c
+++ b/xen/arch/x86/dom0_build.c
@@ -488,6 +488,10 @@ int __init dom0_setup_permissions(struct domain *d)
     rc |= ioports_deny_access(d, 0x40, 0x43);
     /* PIT Channel 2 / PC Speaker Control. */
     rc |= ioports_deny_access(d, 0x61, 0x61);
+
+    /* INIT# and alternative A20M# control. */
+    rc |= ioports_deny_access(d, 0x92, 0x92);
+
     /* ACPI PM Timer. */
     if ( pmtmr_ioport )
         rc |= ioports_deny_access(d, pmtmr_ioport, pmtmr_ioport + 3);