diff --git a/src/mame/drivers/4roses.cpp b/src/mame/drivers/4roses.cpp
index c78616f59b5..0d78c02d030 100644
--- a/src/mame/drivers/4roses.cpp
+++ b/src/mame/drivers/4roses.cpp
@@ -200,9 +200,11 @@ public:
 	void _4roses(machine_config &config);
 	void rugby(machine_config &config);
 private:
+	DECLARE_READ8_MEMBER(_4roses_opcode_r);
 	DECLARE_READ8_MEMBER(rugby_opcode_r);
 
 	void _4roses_map(address_map &map);
+	void _4roses_opcodes_map(address_map &map);
 	void rugby_map(address_map &map);
 	void rugby_opcodes_map(address_map &map);
 
@@ -232,6 +234,22 @@ void _4roses_state::_4roses_map(address_map &map)
 	map(0x6000, 0xffff).rom().region("maincpu", 0x6000);
 }
 
+READ8_MEMBER(_4roses_state::_4roses_opcode_r)
+{
+	uint8_t data = m_maincpu->space(AS_PROGRAM).read_byte(offset);
+	if ((offset & 0x7c00) == 0x6400)
+		data = bitswap<8>(data ^ 0x3f, 3, 4, 2, 5, 1, 6, 0, 7);
+	else if ((offset & 0x7c00) == 0x6000)
+		data = bitswap<8>(data ^ 0x68, 4, 3, 2, 1, 0, 7, 6, 5);
+	return data;
+}
+
+void _4roses_state::_4roses_opcodes_map(address_map &map)
+{
+	map(0x0000, 0x7fff).r(this, FUNC(_4roses_state::_4roses_opcode_r));
+	map(0x8000, 0xffff).rom().region("maincpu", 0x8000);
+}
+
 void _4roses_state::rugby_map(address_map &map)
 {
 	map(0x0000, 0x07ff).ram(); // AM_SHARE("nvram")
@@ -402,6 +420,7 @@ MACHINE_CONFIG_START(_4roses_state::_4roses)
 	/* basic machine hardware */
 	MCFG_CPU_ADD("maincpu", M65C02, MASTER_CLOCK/8) /* 2MHz, guess */
 	MCFG_CPU_PROGRAM_MAP(_4roses_map)
+	MCFG_CPU_OPCODES_MAP(_4roses_opcodes_map)
 
 //  MCFG_NVRAM_ADD_0FILL("nvram")