diff --git a/hw/pc.c b/hw/pc.c
index 07caba7..523db1f 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -435,11 +435,12 @@ static void port92_write(void *opaque, hwaddr addr, uint64_t val,
                          unsigned size)
 {
     Port92State *s = opaque;
+    int oldval = s->outport;
 
     DPRINTF("port92: write 0x%02x\n", val);
     s->outport = val;
     qemu_set_irq(*s->a20_out, (val >> 1) & 1);
-    if (val & 1) {
+    if ((val & 1) && !(oldval & 1)) {
         qemu_system_reset_request();
     }
 }