diff --git a/src/devices/machine/i8255.h b/src/devices/machine/i8255.h
index 76753ba4c47..73dedb92712 100644
--- a/src/devices/machine/i8255.h
+++ b/src/devices/machine/i8255.h
@@ -53,6 +53,8 @@ public:
 	auto out_pa_callback() { return m_out_pa_cb.bind(); }
 	auto out_pb_callback() { return m_out_pb_cb.bind(); }
 	auto out_pc_callback() { return m_out_pc_cb.bind(); }
+
+	// output state when pins are in tri-state, default 0xff
 	auto tri_pa_callback() { return m_tri_pa_cb.bind(); }
 	auto tri_pb_callback() { return m_tri_pb_cb.bind(); }