diff --git a/src/mess/drivers/ymmu100.c b/src/mess/drivers/ymmu100.c
index 05bd1b6d2ce..511840b327c 100644
--- a/src/mess/drivers/ymmu100.c
+++ b/src/mess/drivers/ymmu100.c
@@ -191,9 +191,15 @@ static MACHINE_CONFIG_START( mu100, mu100_state )
 	MCFG_SPEAKER_STANDARD_STEREO("lspeaker", "rspeaker")
 MACHINE_CONFIG_END
 
+#define ROM_LOAD16_WORD_SWAP_BIOS(bios,name,offset,length,hash) \
+		ROMX_LOAD(name, offset, length, hash, ROM_GROUPWORD | ROM_REVERSE | ROM_BIOS(bios+1)) /* Note '+1' */
+
 ROM_START( mu100 )
 	ROM_REGION( 0x200000, "maincpu", 0 )
-	ROM_LOAD16_WORD_SWAP( "xu50720.ic11", 0x000000, 0x200000, CRC(1126a8a4) SHA1(e90b8bd9d14297da26ba12f4d9a4f2d22cd7d34a) ) 
+	ROM_SYSTEM_BIOS( 0, "bios0", "xu50720 (v1.11, Aug. 3, 1999)" )
+	ROM_LOAD16_WORD_SWAP_BIOS( 0, "xu50720.ic11", 0x000000, 0x200000, CRC(1126a8a4) SHA1(e90b8bd9d14297da26ba12f4d9a4f2d22cd7d34a) ) 
+	ROM_SYSTEM_BIOS( 1, "bios1", "xt71420 (v1.05, Sep. 19, 1997)" )
+	ROM_LOAD16_WORD_SWAP_BIOS( 1, "xt71420.ic11", 0x000000, 0x200000, CRC(0e5b3bae) SHA1(3148c5bd59a3d00809d3ab1921216215fe2582c5) ) 
 
 	ROM_REGION( 0x2800000, "waverom", 0 )
 	ROM_LOAD32_WORD( "sx518b0.ic34", 0x000000, 0x400000, CRC(2550d44f) SHA1(fd3cce228c7d389a2fde25c808a5b26080588cba) )