diff --git a/src/devices/sound/ymfm.cpp b/src/devices/sound/ymfm.cpp
index 4c4cc14ac48..55282f3c18b 100644
--- a/src/devices/sound/ymfm.cpp
+++ b/src/devices/sound/ymfm.cpp
@@ -1261,7 +1261,6 @@ ymfm_engine_base<RegisterType>::ymfm_engine_base(device_t &device) :
 	m_irq_mask(STATUS_TIMERA | STATUS_TIMERB),
 	m_irq_state(0),
 	m_busy_end(attotime::zero),
-	m_last_irq_update(attotime::zero),
 	m_timer{ nullptr, nullptr },
 	m_irq_handler(device),
 	m_regdata(RegisterType::REGISTERS),
@@ -1633,17 +1632,7 @@ void ymfm_engine_base<RegisterType>::check_interrupts()
 
 	// if changed, signal the new state
 	if (old_state != m_irq_state && !m_irq_handler.isnull())
-	{
-		// if writes to registers aren't synchronized, it is possible to induce
-		// scheduling errors handling IRQs; ensure that all IRQ handler updates
-		// are monotonically increasing in time
-		attotime curtime = m_device.machine().time();
-		if (m_last_irq_update > curtime)
-			fatalerror("IRQ signalling time went backwards; writes need to be synchronized");
-		m_last_irq_update = curtime;
-
 		m_irq_handler(m_irq_state ? ASSERT_LINE : CLEAR_LINE);
-	}
 }
 
 
diff --git a/src/devices/sound/ymfm.h b/src/devices/sound/ymfm.h
index 18c0afa3d35..be9959a2ef5 100644
--- a/src/devices/sound/ymfm.h
+++ b/src/devices/sound/ymfm.h
@@ -799,7 +799,6 @@ private:
 	u8 m_irq_mask;                   // mask of which bits signal IRQs
 	u8 m_irq_state;                  // current IRQ state
 	attotime m_busy_end;             // end of the busy time
-	attotime m_last_irq_update;      // time of last IRQ update
 	emu_timer *m_timer[2];           // our two timers
 	devcb_write_line m_irq_handler;  // IRQ callback
  	std::unique_ptr<ymfm_channel<RegisterType>> m_channel[RegisterType::CHANNELS]; // channel pointers
diff --git a/src/mame/audio/seibu.cpp b/src/mame/audio/seibu.cpp
index 96bdd5e705b..ad865aa5d90 100644
--- a/src/mame/audio/seibu.cpp
+++ b/src/mame/audio/seibu.cpp
@@ -196,14 +196,9 @@ u8 seibu_sound_device::ym_r(offs_t offset)
 	return m_ym_read_cb(offset);
 }
 
-TIMER_CALLBACK_MEMBER(seibu_sound_device::ym_w_synced)
-{
-	m_ym_write_cb(param >> 8, param & 0xff);
-}
-
 void seibu_sound_device::ym_w(offs_t offset, u8 data)
 {
-	machine().scheduler().synchronize(timer_expired_delegate(FUNC(seibu_sound_device::ym_w_synced), this), data | (offset << 8));
+	m_ym_write_cb(offset, data);
 }
 
 void seibu_sound_device::bank_w(u8 data)
diff --git a/src/mame/audio/seibu.h b/src/mame/audio/seibu.h
index d8da4b6f9d0..1763efb040c 100644
--- a/src/mame/audio/seibu.h
+++ b/src/mame/audio/seibu.h
@@ -80,7 +80,6 @@ protected:
 private:
 	void update_irq_lines(int param);
 	TIMER_CALLBACK_MEMBER(update_irq_synced);
-	TIMER_CALLBACK_MEMBER(ym_w_synced);
 
 	// device callbacks
 	devcb_write_line m_int_cb;