diff --git a/drivers/pnp/interface.c b/drivers/pnp/interface.c
index b09f67d..7a9fb55 100644
--- a/drivers/pnp/interface.c
+++ b/drivers/pnp/interface.c
@@ -90,6 +90,8 @@
 		pnp_printf(buffer, " High-Level");
 	if (irq->flags & IORESOURCE_IRQ_LOWLEVEL)
 		pnp_printf(buffer, " Low-Level");
+	if (irq->flags & IORESOURCE_IRQ_OPTIONAL)
+		pnp_printf(buffer, " (optional)");
 	pnp_printf(buffer, "\n");
 }