diff --git a/hw/misc/mac_via.c b/hw/misc/mac_via.c
index 3c41d6263d..500ece5872 100644
--- a/hw/misc/mac_via.c
+++ b/hw/misc/mac_via.c
@@ -875,6 +875,15 @@ static void via1_auxmode_update(MOS6522Q800VIA1State *v1s)
     if (irq != oldirq) {
         trace_via1_auxmode(irq);
         qemu_set_irq(v1s->auxmode_irq, irq);
+
+        /*
+         * Clear the ADB interrupt. MacOS can leave VIA1B_vADBInt asserted
+         * (low) if a poll sequence doesn't complete before NetBSD disables
+         * interrupts upon boot. Fortunately NetBSD switches to the so-called
+         * "A/UX" interrupt mode after it initialises, so we can use this as
+         * a convenient place to clear the ADB interrupt for now.
+         */
+        s->b |= VIA1B_vADBInt;
     }
 }