diff --git a/src/device/serial.c b/src/device/serial.c
index 25c9c0a49..3de0c6826 100644
--- a/src/device/serial.c
+++ b/src/device/serial.c
@@ -128,7 +128,7 @@ serial_update_ints(serial_t *dev)
 	dev->iir = 0;
     }
 
-    if (stat && ((dev->mctrl & 8) || (dev->type == SERIAL_8250_PCJR))) {
+    if (stat && (dev->irq != 0xff) && ((dev->mctrl & 8) || (dev->type == SERIAL_8250_PCJR))) {
 	if (dev->type >= SERIAL_NS16450)
 		picintlevel(1 << dev->irq);
 	else
@@ -615,7 +615,7 @@ serial_remove(serial_t *dev)
 
 
 void
-serial_setup(serial_t *dev, uint16_t addr, int irq)
+serial_setup(serial_t *dev, uint16_t addr, uint8_t irq)
 {
     serial_log("Adding serial port %i at %04X...\n", dev->inst, addr);
 
diff --git a/src/include/86box/serial.h b/src/include/86box/serial.h
index 59e179903..0b6b99aa5 100644
--- a/src/include/86box/serial.h
+++ b/src/include/86box/serial.h
@@ -77,7 +77,7 @@ extern serial_t *	serial_attach(int port,
 			      void *priv);
 extern void	serial_remove(serial_t *dev);
 extern void	serial_set_type(serial_t *dev, int type);
-extern void	serial_setup(serial_t *dev, uint16_t addr, int irq);
+extern void	serial_setup(serial_t *dev, uint16_t addr, uint8_t irq);
 extern void	serial_clear_fifo(serial_t *dev);
 extern void	serial_write_fifo(serial_t *dev, uint8_t dat);
 extern void	serial_set_next_inst(int ni);