diff --git a/hw/piix_pci.c b/hw/piix_pci.c
index 8c00f0d136..3c04e3a08f 100644
--- a/hw/piix_pci.c
+++ b/hw/piix_pci.c
@@ -208,6 +208,7 @@ static void piix3_set_irq(qemu_irq *pic, int irq_num, int level)
 {
     int i, pic_irq, pic_level;
 
+    piix3_dev->config[0x60 + irq_num] &= ~0x80;   // enable bit
     pci_irq_levels[irq_num] = level;
 
     /* now we change the pic irq level according to the piix irq mappings */