diff --git a/src/mame/sega/segas16a.cpp b/src/mame/sega/segas16a.cpp
index a759f9c175e..0f2af1ea4d5 100644
--- a/src/mame/sega/segas16a.cpp
+++ b/src/mame/sega/segas16a.cpp
@@ -1997,6 +1997,9 @@ void segas16a_state::system16a(machine_config &config)
 	m_i8255->out_pa_callback().set("soundlatch", FUNC(generic_latch_8_device::write));
 	m_i8255->out_pb_callback().set(FUNC(segas16a_state::misc_control_w));
 	m_i8255->out_pc_callback().set(FUNC(segas16a_state::tilemap_sound_w));
+	m_i8255->tri_pa_callback().set_constant(0);
+	m_i8255->tri_pb_callback().set_constant(0);
+	m_i8255->tri_pc_callback().set_constant(0);
 
 	// video hardware
 	SCREEN(config, m_screen, SCREEN_TYPE_RASTER);
@@ -4017,7 +4020,6 @@ GAME( 1987, timescan1,  timescan, system16a_fd1089b,        timescan,        seg
 GAME( 1988, wb31,       wb3,      system16a_fd1094_no7751,  wb3,             segas16a_state,            init_generic,     ROT0,   "Sega / Westone", "Wonder Boy III - Monster Lair (set 1, Japan, System 16A) (FD1094 317-0084)", MACHINE_SUPPORTS_SAVE )
 GAME( 1988, wb35,       wb3,      system16a_fd1089a_no7751, wb3,             segas16a_state,            init_generic,     ROT0,   "Sega / Westone", "Wonder Boy III - Monster Lair (set 5, Japan, System 16A) (FD1089A 317-0086)", MACHINE_SUPPORTS_SAVE )
 
-
 GAME( 1988, wb31d,      wb3,      system16a_no7751,         wb3,             segas16a_state,            init_generic,     ROT0,   "bootleg", "Wonder Boy III - Monster Lair (set 1, Japan, System 16A) (bootleg of FD1094 317-0084 set)", MACHINE_SUPPORTS_SAVE )
 GAME( 1988, wb35d,      wb3,      system16a_no7751,         wb3,             segas16a_state,            init_generic,     ROT0,   "bootleg", "Wonder Boy III - Monster Lair (set 5, Japan, System 16A) (bootleg of FD1089A 317-0086 set)", MACHINE_SUPPORTS_SAVE )
 GAME( 1987, shinobi1d,  shinobi,  system16a,                shinobi,         segas16a_state,            init_generic,     ROT0,   "bootleg", "Shinobi (set 1, System 16A) (bootleg of FD1094 317-0050 set)", MACHINE_SUPPORTS_SAVE )
diff --git a/src/mame/sega/segas16a.h b/src/mame/sega/segas16a.h
index 15fba62538c..2ae6c1bc1d7 100644
--- a/src/mame/sega/segas16a.h
+++ b/src/mame/sega/segas16a.h
@@ -175,15 +175,15 @@ private:
 	lamp_changed_delegate   m_lamp_changed_w;
 
 	// internal state
-	emu_timer              * m_i8751_sync_timer = nullptr;
-	uint8_t                  m_video_control = 0;
-	uint8_t                  m_mcu_control = 0;
-	uint8_t                  m_n7751_command = 0;
-	uint32_t                 m_n7751_rom_address = 0;
-	uint8_t                  m_last_buttons1 = 0;
-	uint8_t                  m_last_buttons2 = 0;
-	uint8_t                  m_read_port = 0;
-	uint8_t                  m_mj_input_num = 0;
+	emu_timer              * m_i8751_sync_timer;
+	uint8_t                  m_video_control;
+	uint8_t                  m_mcu_control;
+	uint8_t                  m_n7751_command;
+	uint32_t                 m_n7751_rom_address;
+	uint8_t                  m_last_buttons1;
+	uint8_t                  m_last_buttons2;
+	uint8_t                  m_read_port;
+	uint8_t                  m_mj_input_num;
 	optional_ioport_array<6> m_mj_inputs;
 	output_finder<2> m_lamps;
 };