diff --git a/src/mame/drivers/vertigo.c b/src/mame/drivers/vertigo.c
index 4f5af1c2429..1d46f0b33da 100644
--- a/src/mame/drivers/vertigo.c
+++ b/src/mame/drivers/vertigo.c
@@ -32,7 +32,7 @@ static ADDRESS_MAP_START( vertigo_map, ADDRESS_SPACE_PROGRAM, 16 )
 	AM_RANGE(0x004020, 0x00402f) AM_READ(vertigo_coin_r) AM_MIRROR(0x001000)
 	AM_RANGE(0x004030, 0x00403f) AM_READ(input_port_3_word_r) AM_MIRROR(0x001000)
 	AM_RANGE(0x004040, 0x00404f) AM_READ(vertigo_sio_r) AM_MIRROR(0x001000)
-	AM_RANGE(0x004050, 0x00405f) AM_WRITE(vertigo_audio_w) AM_MIRROR(0x001000)
+	AM_RANGE(0x004050, 0x00405f) AM_READWRITE(SMH_RAM, vertigo_audio_w) AM_BASE(((UINT16 **) &exidy440_sound_command)) AM_MIRROR(0x001000)
 	AM_RANGE(0x004060, 0x00406f) AM_WRITE(vertigo_motor_w) AM_MIRROR(0x001000)
 	AM_RANGE(0x004070, 0x00407f) AM_WRITE(vertigo_wsot_w) AM_MIRROR(0x001000)
 	AM_RANGE(0x006000, 0x006007) AM_READWRITE(pit8253_0_lsb_r, pit8253_0_lsb_w)