diff --git a/src/mess/drivers/hh_sm510.c b/src/mess/drivers/hh_sm510.c
index 0f4bc9b7ef0..fe7178981c2 100644
--- a/src/mess/drivers/hh_sm510.c
+++ b/src/mess/drivers/hh_sm510.c
@@ -176,22 +176,20 @@ WRITE8_MEMBER(ktopgun_state::speaker_w)
 
 static INPUT_PORTS_START( ktopgun )
 	PORT_START("IN.0")
-	PORT_BIT( 0x01, IP_ACTIVE_HIGH, IPT_BUTTON1 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL)
-	PORT_BIT( 0x02, IP_ACTIVE_HIGH, IPT_BUTTON2 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL)
-	PORT_BIT( 0x04, IP_ACTIVE_HIGH, IPT_BUTTON3 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL)
-	PORT_BIT( 0x08, IP_ACTIVE_HIGH, IPT_BUTTON4 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL)
-
-	PORT_START("IN.1")
 	PORT_BIT( 0x01, IP_ACTIVE_HIGH, IPT_JOYSTICK_LEFT ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL)
 	PORT_BIT( 0x02, IP_ACTIVE_HIGH, IPT_JOYSTICK_UP ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL)
 	PORT_BIT( 0x04, IP_ACTIVE_HIGH, IPT_JOYSTICK_DOWN ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL)
 	PORT_BIT( 0x08, IP_ACTIVE_HIGH, IPT_JOYSTICK_RIGHT ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL)
 
+	PORT_START("IN.1")
+	PORT_BIT( 0x01, IP_ACTIVE_HIGH, IPT_BUTTON1 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL) // sel
+	PORT_BIT( 0x02, IP_ACTIVE_HIGH, IPT_BUTTON2 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL) // sound on/off
+	PORT_BIT( 0x04, IP_ACTIVE_HIGH, IPT_BUTTON3 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL) // off
+	PORT_BIT( 0x08, IP_ACTIVE_HIGH, IPT_BUTTON4 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL) // fire
+
 	PORT_START("IN.2")
-	PORT_BIT( 0x01, IP_ACTIVE_HIGH, IPT_BUTTON5 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL)
-	PORT_BIT( 0x02, IP_ACTIVE_HIGH, IPT_BUTTON6 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL)
-	PORT_BIT( 0x04, IP_ACTIVE_HIGH, IPT_BUTTON7 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL)
-	PORT_BIT( 0x08, IP_ACTIVE_HIGH, IPT_BUTTON8 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL)
+	PORT_BIT( 0x01, IP_ACTIVE_HIGH, IPT_BUTTON5 ) PORT_CHANGED_MEMBER(DEVICE_SELF, hh_sm510_state, input_changed, NULL) // on
+	PORT_BIT( 0x0e, IP_ACTIVE_HIGH, IPT_UNUSED )
 INPUT_PORTS_END
 
 static MACHINE_CONFIG_START( ktopgun, ktopgun_state )