diff --git a/sys/pc98/cbus/sio.c b/sys/pc98/cbus/sio.c
index e2f6916dd374..ce35e3f5a747 100644
--- a/sys/pc98/cbus/sio.c
+++ b/sys/pc98/cbus/sio.c
@@ -1948,6 +1948,7 @@ sioopen(dev, flag, mode, td)
 		 * XXX we should goto open_top if comparam() slept.
 		 */
 		if (com->hasfifo) {
+			int i;
 			/*
 			 * (Re)enable and drain fifos.
 			 *
@@ -1959,7 +1960,7 @@ sioopen(dev, flag, mode, td)
 			 * and to handle races between enabling and fresh
 			 * input.
 			 */
-			while (TRUE) {
+			for (i = 0; i < 500; i++) {
 				sio_setreg(com, com_fifo,
 					   FIFO_RCV_RST | FIFO_XMT_RST
 					   | com->fifo_image);
@@ -1992,6 +1993,10 @@ sioopen(dev, flag, mode, td)
 				DELAY(50);
 				(void) inb(com->data_port);
 			}
+			if (i == 500) {
+				error = EIO;
+				goto out;
+			}
 		}
 
 		mtx_lock_spin(&sio_lock);
diff --git a/sys/pc98/pc98/sio.c b/sys/pc98/pc98/sio.c
index e2f6916dd374..ce35e3f5a747 100644
--- a/sys/pc98/pc98/sio.c
+++ b/sys/pc98/pc98/sio.c
@@ -1948,6 +1948,7 @@ sioopen(dev, flag, mode, td)
 		 * XXX we should goto open_top if comparam() slept.
 		 */
 		if (com->hasfifo) {
+			int i;
 			/*
 			 * (Re)enable and drain fifos.
 			 *
@@ -1959,7 +1960,7 @@ sioopen(dev, flag, mode, td)
 			 * and to handle races between enabling and fresh
 			 * input.
 			 */
-			while (TRUE) {
+			for (i = 0; i < 500; i++) {
 				sio_setreg(com, com_fifo,
 					   FIFO_RCV_RST | FIFO_XMT_RST
 					   | com->fifo_image);
@@ -1992,6 +1993,10 @@ sioopen(dev, flag, mode, td)
 				DELAY(50);
 				(void) inb(com->data_port);
 			}
+			if (i == 500) {
+				error = EIO;
+				goto out;
+			}
 		}
 
 		mtx_lock_spin(&sio_lock);