diff --git a/src/emu/natkeyboard.cpp b/src/emu/natkeyboard.cpp
index c3c05f0e9fb..7d154787c0c 100644
--- a/src/emu/natkeyboard.cpp
+++ b/src/emu/natkeyboard.cpp
@@ -602,7 +602,7 @@ void natural_keyboard::build_codes(ioport_manager &manager)
 {
 	// find all shift keys
 	unsigned mask = 0;
-	ioport_field *shift[SHIFT_COUNT];
+	std::array<ioport_field *, SHIFT_COUNT> shift;
 	std::fill(std::begin(shift), std::end(shift), nullptr);
 	for (auto const &port : manager.ports())
 	{
@@ -656,7 +656,6 @@ void natural_keyboard::build_codes(ioport_manager &manager)
 											newcode.field[fieldnum++] = shift[i];
 									}
 
-									assert(fieldnum < ARRAY_LENGTH(newcode.field));
 									newcode.field[fieldnum] = &field;
 									if (m_keycode_map.end() == found)
 										m_keycode_map.emplace(code, newcode);
@@ -795,8 +794,6 @@ void natural_keyboard::timer(void *ptr, int param)
 		{
 			do
 			{
-				assert(m_fieldnum < ARRAY_LENGTH(code->field));
-
 				ioport_field *const field = code->field[m_fieldnum];
 				if (field)
 				{
@@ -807,8 +804,8 @@ void natural_keyboard::timer(void *ptr, int param)
 						field->set_value(!field->digital_value());
 				}
 			}
-			while (code->field[m_fieldnum] && (++m_fieldnum < ARRAY_LENGTH(code->field)) && m_status_keydown);
-			advance = (m_fieldnum >= ARRAY_LENGTH(code->field)) || !code->field[m_fieldnum];
+			while (code->field[m_fieldnum] && (++m_fieldnum < code->field.size()) && m_status_keydown);
+			advance = (m_fieldnum >= code->field.size()) || !code->field[m_fieldnum];
 		}
 		else
 		{
@@ -902,7 +899,7 @@ void natural_keyboard::dump(std::ostream &str) const
 		util::stream_format(str, "%-*s", left_column_width, description);
 
 		// identify the keys used
-		for (std::size_t field = 0; (ARRAY_LENGTH(code.second.field) > field) && code.second.field[field]; ++field)
+		for (std::size_t field = 0; (code.second.field.size() > field) && code.second.field[field]; ++field)
 			util::stream_format(str, "%s'%s'", first ? "" : ", ", code.second.field[field]->name());
 
 		// carriage return
diff --git a/src/emu/natkeyboard.h b/src/emu/natkeyboard.h
index fa3df156285..d8cc9cfb8ff 100644
--- a/src/emu/natkeyboard.h
+++ b/src/emu/natkeyboard.h
@@ -72,8 +72,8 @@ private:
 	// internal keyboard code information
 	struct keycode_map_entry
 	{
-		ioport_field *  field[SHIFT_COUNT + 1];
-		unsigned        shift;
+		std::array<ioport_field *, SHIFT_COUNT + 1>	field;
+		unsigned									shift;
 	};
 	typedef std::unordered_map<char32_t, keycode_map_entry> keycode_map;