diff --git a/hw/ppc/mac_newworld.c b/hw/ppc/mac_newworld.c
index b8189bf..b2ec372 100644
--- a/hw/ppc/mac_newworld.c
+++ b/hw/ppc/mac_newworld.c
@@ -155,13 +155,12 @@
     memory_region_add_subregion(get_system_memory(), 0, machine->ram);
 
     /* allocate and load BIOS */
-    memory_region_init_ram(bios, NULL, "ppc_core99.bios", BIOS_SIZE,
+    memory_region_init_rom(bios, NULL, "ppc_core99.bios", BIOS_SIZE,
                            &error_fatal);
 
     if (bios_name == NULL)
         bios_name = PROM_FILENAME;
     filename = qemu_find_file(QEMU_FILE_TYPE_BIOS, bios_name);
-    memory_region_set_readonly(bios, true);
     memory_region_add_subregion(get_system_memory(), PROM_ADDR, bios);
 
     /* Load OpenBIOS (ELF) */
diff --git a/hw/ppc/mac_oldworld.c b/hw/ppc/mac_oldworld.c
index 440c406..faaa165 100644
--- a/hw/ppc/mac_oldworld.c
+++ b/hw/ppc/mac_oldworld.c
@@ -129,13 +129,12 @@
     memory_region_add_subregion(sysmem, 0, machine->ram);
 
     /* allocate and load BIOS */
-    memory_region_init_ram(bios, NULL, "ppc_heathrow.bios", BIOS_SIZE,
+    memory_region_init_rom(bios, NULL, "ppc_heathrow.bios", BIOS_SIZE,
                            &error_fatal);
 
     if (bios_name == NULL)
         bios_name = PROM_FILENAME;
     filename = qemu_find_file(QEMU_FILE_TYPE_BIOS, bios_name);
-    memory_region_set_readonly(bios, true);
     memory_region_add_subregion(sysmem, PROM_ADDR, bios);
 
     /* Load OpenBIOS (ELF) */