diff --git a/src/mame/drivers/bzone.cpp b/src/mame/drivers/bzone.cpp
index f95bf75f3d7..2da43382822 100644
--- a/src/mame/drivers/bzone.cpp
+++ b/src/mame/drivers/bzone.cpp
@@ -355,7 +355,7 @@ ADDRESS_MAP_END
 	PORT_BIT( 0x02, IP_ACTIVE_LOW, IPT_COIN2 )\
 	PORT_BIT( 0x0c, IP_ACTIVE_LOW, IPT_UNUSED )\
 	PORT_SERVICE( 0x10, IP_ACTIVE_LOW )\
-	PORT_BIT( 0x20, IP_ACTIVE_LOW, IPT_SERVICE ) PORT_NAME("Diagnostic Step") PORT_CODE(KEYCODE_F1)\
+	PORT_BIT( 0x20, IP_ACTIVE_LOW, IPT_SERVICE1 ) PORT_NAME("Diagnostic Step") \
 	/* bit 6 is the VG HALT bit. We set it to "low" */\
 	/* per default (busy vector processor). */\
 	PORT_BIT( 0x40, IP_ACTIVE_HIGH, IPT_SPECIAL ) PORT_CUSTOM_MEMBER("avg", avg_bzone_device, done_r, nullptr)\