diff --git a/src/mame/sgi/ip20.cpp b/src/mame/sgi/ip20.cpp
index 5d2fdee4de4..7088bbc7cd1 100644
--- a/src/mame/sgi/ip20.cpp
+++ b/src/mame/sgi/ip20.cpp
@@ -282,7 +282,11 @@ void ip20_state::ip20(machine_config &config)
 
 ROM_START(indigo_r4000)
 	ROM_REGION64_BE(0x80000, "prom", 0)
-	ROMX_LOAD("ip20prom.070-8116-004.bin", 0x000000, 0x080000, CRC(940d960e) SHA1(596aba530b53a147985ff3f6f853471ce48c866c), ROM_GROUPDWORD | ROM_REVERSE)
+	ROM_SYSTEM_BIOS(0, "405g-rev-b", "SGI Version 4.0.5G Rev B IP20, Nov 10, 1992") // dumped over serial connection from boot monitor and swapped
+	ROMX_LOAD("ip20prom.070-8116-005.bin", 0x000000, 0x080000, CRC(1875b645) SHA1(52f5d7baea3d1bc720eb2164104c177e23504345), ROM_GROUPDWORD | ROM_REVERSE | ROM_BIOS(0))
+
+	ROM_SYSTEM_BIOS(1, "405d-rev-a", "SGI Version 4.0.5D Rev A IP20, Aug 19, 1992")
+	ROMX_LOAD("ip20prom.070-8116-004.bin", 0x000000, 0x080000, CRC(940d960e) SHA1(596aba530b53a147985ff3f6f853471ce48c866c), ROM_GROUPDWORD | ROM_REVERSE | ROM_BIOS(1))
 
 	// hand-made content sets eaddr 08:00:69:12:34:56 and netaddr 192.168.137.2
 	ROM_REGION16_LE(0x100, "nvram", 0)