diff --git a/src/mame/drivers/r9751.cpp b/src/mame/drivers/r9751.cpp
index 5cd2834c653..dbb2efa2bb6 100644
--- a/src/mame/drivers/r9751.cpp
+++ b/src/mame/drivers/r9751.cpp
@@ -524,7 +524,10 @@ MACHINE_CONFIG_END
 ROM_START(r9751)
 	ROM_REGION32_BE(0x00010000, "prom", 0)
 	ROM_SYSTEM_BIOS(0, "prom34",  "PROM Version 3.4")
-	ROMX_LOAD( "p-n_98d4643__abaco_v3.4__(49fe7a)__j221.27512.bin", 0x0000, 0x10000, CRC(9fb19a85) SHA1(c861e15a2fc9a4ef689c2034c53fbb36f17f7da6), ROM_GROUPWORD | ROM_BIOS(1) ) // Label: "P/N 98D4643 // ABACO V3.4 // (49FE7A) // J221" 27128 @Unknown
+	ROMX_LOAD( "p-n_98d4643__abaco_v3.4__(49fe7a)__j221.27512.bin", 0x0000, 0x10000, CRC(9fb19a85) SHA1(c861e15a2fc9a4ef689c2034c53fbb36f17f7da6), ROM_GROUPWORD | ROM_BIOS(1) ) // Label: "P/N 98D4643 // ABACO V3.4 // (49FE7A) // J221" 27512 @Unknown
+
+	ROM_SYSTEM_BIOS(1, "prom42", "PROM Version 4.2")
+	ROMX_LOAD( "98d5731__zebra_v4.2__4cd79d.u5", 0x0000, 0x10000, CRC(e640f8df) SHA1(a9e4fa271d7f2f3a134e2120932ec088d5b8b007), ROM_GROUPWORD | ROM_BIOS(2) ) // Label: 98D5731 // ZEBRA V4.2 // 4CD79D 27512 @Unknown
 ROM_END