diff --git a/src/devices/machine/7200fifo.cpp b/src/devices/machine/7200fifo.cpp
index a5af4967dc1..e9cb45f66a7 100644
--- a/src/devices/machine/7200fifo.cpp
+++ b/src/devices/machine/7200fifo.cpp
@@ -132,7 +132,7 @@ void fifo7200_device::fifo_write(uint16_t data)
 		m_ff_handler(!m_ff);
 	}
 
-	else if (((m_read_ptr + 1 + m_ram_size / 2) % m_ram_size) == m_write_ptr)
+	else if (!m_hf && (fifo_used() >= m_ram_size / 2))
 	{
 		m_hf = 1;
 		m_hf_handler(!m_hf);
@@ -166,12 +166,30 @@ uint16_t fifo7200_device::fifo_read()
 			m_ef_handler(!m_ef);
 		}
 
-		else if (((m_read_ptr + m_ram_size / 2) % m_ram_size) == m_write_ptr)
+		else if (m_hf && (fifo_used() < m_ram_size / 2))
 		{
 			m_hf = 0;
 			m_hf_handler(!m_hf);
 		}
 	}
+	return ret;
+}
+
+int fifo7200_device::fifo_used()
+{
+	int ret = m_ram_size;
+
+	if (!m_ff)
+	{
+		if (m_write_ptr >= m_read_ptr)
+		{
+			ret = m_write_ptr - m_read_ptr;
+		}
+		else
+		{
+			ret = m_ram_size + m_write_ptr - m_read_ptr;
+		}
+	}
 
 	return ret;
 }
diff --git a/src/devices/machine/7200fifo.h b/src/devices/machine/7200fifo.h
index 4ed323a98ac..6609d4efad6 100644
--- a/src/devices/machine/7200fifo.h
+++ b/src/devices/machine/7200fifo.h
@@ -88,6 +88,7 @@ protected:
 private:
 	void fifo_write(uint16_t data);
 	uint16_t fifo_read();
+	int fifo_used();
 
 	std::vector<uint16_t> m_buffer;
 	const int m_ram_size;