diff --git a/src/mame/drivers/model1.cpp b/src/mame/drivers/model1.cpp
index 234d847f867..f39fa44ab10 100644
--- a/src/mame/drivers/model1.cpp
+++ b/src/mame/drivers/model1.cpp
@@ -1668,6 +1668,7 @@ MACHINE_CONFIG_END
 
 static ADDRESS_MAP_START( polhemus_map, AS_PROGRAM, 16, model1_state )
 	ADDRESS_MAP_GLOBAL_MASK(0xfffff)
+	AM_RANGE(0x00000, 0x03fff) AM_RAM
 	AM_RANGE(0xf8000, 0xfffff) AM_ROM AM_REGION("polhemus", 0)
 ADDRESS_MAP_END