diff --git a/src/mame/drivers/proconn.c b/src/mame/drivers/proconn.c
index dddf27aa694..bbb29af5f39 100644
--- a/src/mame/drivers/proconn.c
+++ b/src/mame/drivers/proconn.c
@@ -366,7 +366,7 @@ static MACHINE_CONFIG_START( proconn, proconn_state )
 	MCFG_DEVICE_ADD("z80ctc", Z80CTC, 4000000)
 	MCFG_Z80CTC_INTR_CB(INPUTLINE("maincpu", INPUT_LINE_IRQ0))
 
-	MCFG_Z80SIO0_ADD( "z80sio",   4000000, NULL, NULL, NULL, NULL ) /* ?? Mhz */
+	MCFG_Z80SIO0_ADD( "z80sio",   4000000, 0, 0, 0, 0 ) /* ?? Mhz */
 
 	MCFG_SPEAKER_STANDARD_STEREO("lspeaker", "rspeaker")