diff --git a/hw/acpi_piix4.c b/hw/acpi_piix4.c
index 350558b8594bd46cf76037ad611f5286607594d2..03bd768366dfdfee74ea7d0bc02e849dc16e151b 100644
--- a/hw/acpi_piix4.c
+++ b/hw/acpi_piix4.c
@@ -23,6 +23,7 @@
 #include "acpi.h"
 #include "sysemu.h"
 #include "range.h"
+#include "ioport.h"
 
 //#define DEBUG
 
@@ -63,6 +64,7 @@ typedef struct PIIX4PMState {
     qemu_irq irq;
     qemu_irq smi_irq;
     int kvm_enabled;
+    Notifier machine_ready;
 
     /* for pci hotplug */
     ACPIGPE gpe;
@@ -311,6 +313,19 @@ static void piix4_powerdown(void *opaque, int irq, int power_failing)
     acpi_pm1_evt_power_down(pm1a, tmr);
 }
 
+static void piix4_pm_machine_ready(struct Notifier* n)
+{
+    PIIX4PMState *s = container_of(n, PIIX4PMState, machine_ready);
+    uint8_t *pci_conf;
+
+    pci_conf = s->dev.config;
+    pci_conf[0x5f] = (isa_is_ioport_assigned(0x378) ? 0x80 : 0) | 0x10;
+    pci_conf[0x63] = 0x60;
+    pci_conf[0x67] = (isa_is_ioport_assigned(0x3f8) ? 0x08 : 0) |
+	(isa_is_ioport_assigned(0x2f8) ? 0x90 : 0);
+
+}
+
 static int piix4_pm_initfn(PCIDevice *dev)
 {
     PIIX4PMState *s = DO_UPCAST(PIIX4PMState, dev, dev);
@@ -337,11 +352,6 @@ static int piix4_pm_initfn(PCIDevice *dev)
 
     /* XXX: which specification is used ? The i82731AB has different
        mappings */
-    pci_conf[0x5f] = (parallel_hds[0] != NULL ? 0x80 : 0) | 0x10;
-    pci_conf[0x63] = 0x60;
-    pci_conf[0x67] = (serial_hds[0] != NULL ? 0x08 : 0) |
-	(serial_hds[1] != NULL ? 0x90 : 0);
-
     pci_conf[0x90] = s->smb_io_base | 1;
     pci_conf[0x91] = s->smb_io_base >> 8;
     pci_conf[0xd2] = 0x09;
@@ -354,6 +364,8 @@ static int piix4_pm_initfn(PCIDevice *dev)
     qemu_system_powerdown = *qemu_allocate_irqs(piix4_powerdown, s, 1);
 
     pm_smbus_init(&s->dev.qdev, &s->smb);
+    s->machine_ready.notify = piix4_pm_machine_ready;
+    qemu_add_machine_init_done_notifier(&s->machine_ready);
     qemu_register_reset(piix4_reset, s);
     piix4_acpi_system_hot_add_init(dev->bus, s);
 
diff --git a/ioport.c b/ioport.c
index 2e971fa3e5cd89ff3c8c175214e15d7632c71b42..0d2611d14298f7747b8b71aaad5a0d184584aad8 100644
--- a/ioport.c
+++ b/ioport.c
@@ -245,18 +245,25 @@ void isa_unassign_ioport(pio_addr_t start, int length)
     int i;
 
     for(i = start; i < start + length; i++) {
-        ioport_read_table[0][i] = default_ioport_readb;
-        ioport_read_table[1][i] = default_ioport_readw;
-        ioport_read_table[2][i] = default_ioport_readl;
+        ioport_read_table[0][i] = NULL;
+        ioport_read_table[1][i] = NULL;
+        ioport_read_table[2][i] = NULL;
 
-        ioport_write_table[0][i] = default_ioport_writeb;
-        ioport_write_table[1][i] = default_ioport_writew;
-        ioport_write_table[2][i] = default_ioport_writel;
+        ioport_write_table[0][i] = NULL;
+        ioport_write_table[1][i] = NULL;
+        ioport_write_table[2][i] = NULL;
 
         ioport_opaque[i] = NULL;
     }
 }
 
+bool isa_is_ioport_assigned(pio_addr_t start)
+{
+    return (ioport_read_table[0][start] || ioport_write_table[0][start] ||
+	    ioport_read_table[1][start] || ioport_write_table[1][start] ||
+	    ioport_read_table[2][start] || ioport_write_table[2][start]);
+}
+
 /***********************************************************/
 
 void cpu_outb(pio_addr_t addr, uint8_t val)
diff --git a/ioport.h b/ioport.h
index 5ae62a3a2c712b9b322d8011d7052fb7cdc94380..82ffd9d81a96831544aa742e67f9266af64d7415 100644
--- a/ioport.h
+++ b/ioport.h
@@ -43,7 +43,7 @@ int register_ioport_read(pio_addr_t start, int length, int size,
 int register_ioport_write(pio_addr_t start, int length, int size,
                           IOPortWriteFunc *func, void *opaque);
 void isa_unassign_ioport(pio_addr_t start, int length);
-
+bool isa_is_ioport_assigned(pio_addr_t start);
 
 void cpu_outb(pio_addr_t addr, uint8_t val);
 void cpu_outw(pio_addr_t addr, uint16_t val);