diff --git a/src/mame/drivers/jpmimpct.c b/src/mame/drivers/jpmimpct.c
index 5455619bb8a..c0ce66ea8c5 100644
--- a/src/mame/drivers/jpmimpct.c
+++ b/src/mame/drivers/jpmimpct.c
@@ -615,7 +615,7 @@ static ADDRESS_MAP_START( tms_program_map, AS_PROGRAM, 16 )
 	AM_RANGE(0x00800000, 0x00ffffff) AM_MIRROR(0xf8000000) AM_ROM AM_REGION("user1", 0x100000)
 	AM_RANGE(0x02000000, 0x027fffff) AM_MIRROR(0xf8000000) AM_ROM AM_REGION("user1", 0)
 //	AM_RANGE(0x01000000, 0x0100003f) AM_MIRROR(0xf87fffc0) AM_READWRITE(jpmimpct_bt477_r, jpmimpct_bt477_w)
-	AM_RANGE(0x01000000, 0xf97fffff) AM_READWRITE(jpmimpct_bt477_r, jpmimpct_bt477_w)
+	AM_RANGE(0x01000000, 0x017fffff) AM_MIRROR(0xf8000000) AM_MASK(0x1f) AM_READWRITE(jpmimpct_bt477_r, jpmimpct_bt477_w)
 	AM_RANGE(0x07800000, 0x07bfffff) AM_MIRROR(0xf8400000) AM_RAM
 ADDRESS_MAP_END