diff --git a/src/mess/drivers/isbc.c b/src/mess/drivers/isbc.c
index beb56fe43a5..d88843cd5ee 100644
--- a/src/mess/drivers/isbc.c
+++ b/src/mess/drivers/isbc.c
@@ -74,6 +74,7 @@ static ADDRESS_MAP_START(isbc286_mem, AS_PROGRAM, 16, isbc_state)
 	ADDRESS_MAP_UNMAP_HIGH
 	AM_RANGE(0x00000, 0xdffff) AM_RAM
 	AM_RANGE(0xe0000, 0xfffff) AM_ROM AM_REGION("user1",0)
+	AM_RANGE(0xfe0000, 0xffffff) AM_ROM AM_REGION("user1",0)
 ADDRESS_MAP_END
 
 static ADDRESS_MAP_START(isbc286_io, AS_IO, 16, isbc_state)
@@ -84,6 +85,7 @@ static ADDRESS_MAP_START(isbc2861_mem, AS_PROGRAM, 16, isbc_state)
 	ADDRESS_MAP_UNMAP_HIGH
 	AM_RANGE(0x00000, 0xeffff) AM_RAM
 	AM_RANGE(0xf0000, 0xfffff) AM_ROM AM_REGION("user1",0)
+	AM_RANGE(0xff0000, 0xffffff) AM_ROM AM_REGION("user1",0)
 ADDRESS_MAP_END
 
 static ADDRESS_MAP_START(isbc2861_io, AS_IO, 16, isbc_state)
diff --git a/src/mess/drivers/pc.c b/src/mess/drivers/pc.c
index 50b18e6ba45..6d530909ef1 100644
--- a/src/mess/drivers/pc.c
+++ b/src/mess/drivers/pc.c
@@ -404,6 +404,7 @@ ADDRESS_MAP_END
 
 
 static ADDRESS_MAP_START(tandy1000_286_map, AS_PROGRAM, 16, pc_state )
+	ADDRESS_MAP_GLOBAL_MASK(0x000fffff)
 	AM_RANGE(0x00000, 0x9ffff) AM_RAMBANK("bank10")
 	AM_RANGE(0xa0000, 0xaffff) AM_RAM
 	AM_RANGE(0xb0000, 0xb7fff) AM_NOP