diff --git a/sys/dev/ahci/ahci.c b/sys/dev/ahci/ahci.c
index a1406f60b7b..ee0e95795a9 100644
--- a/sys/dev/ahci/ahci.c
+++ b/sys/dev/ahci/ahci.c
@@ -466,6 +466,7 @@ ahci_intr(void *data)
 	} else {	/* AHCI_IRQ_MODE_AFTER */
 		unit = irq->r_irq_rid - 1;
 		is = ATA_INL(ctlr->r_mem, AHCI_IS);
+		is &= (0xffffffff << unit);
 	}
 	/* CCC interrupt is edge triggered. */
 	if (ctlr->ccc)