diff --git a/src/mame/drivers/system1.cpp b/src/mame/drivers/system1.cpp
index 95e8486aec0..a3697e9df01 100644
--- a/src/mame/drivers/system1.cpp
+++ b/src/mame/drivers/system1.cpp
@@ -817,8 +817,8 @@ ADDRESS_MAP_END
 static ADDRESS_MAP_START( sound_map, AS_PROGRAM, 8, system1_state )
 	AM_RANGE(0x0000, 0x7fff) AM_ROM
 	AM_RANGE(0x8000, 0x87ff) AM_MIRROR(0x1800) AM_RAM
-	AM_RANGE(0xa000, 0xa003) AM_MIRROR(0x1fff) AM_DEVWRITE("sn1", sn76489a_device, write)
-	AM_RANGE(0xc000, 0xc003) AM_MIRROR(0x1fff) AM_DEVWRITE("sn2", sn76489a_device, write)
+	AM_RANGE(0xa000, 0xa000) AM_MIRROR(0x1fff) AM_DEVWRITE("sn1", sn76489a_device, write)
+	AM_RANGE(0xc000, 0xc000) AM_MIRROR(0x1fff) AM_DEVWRITE("sn2", sn76489a_device, write)
 	AM_RANGE(0xe000, 0xe000) AM_MIRROR(0x1fff) AM_READ(sound_data_r)
 ADDRESS_MAP_END