diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 22e16031b0..59435390ba 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1443,6 +1443,9 @@ void pc_memory_init(PCMachineState *pcms,
     option_rom_mr = g_malloc(sizeof(*option_rom_mr));
     memory_region_init_ram(option_rom_mr, NULL, "pc.rom", PC_ROM_SIZE,
                            &error_fatal);
+    if (pcmc->pci_enabled) {
+        memory_region_set_readonly(option_rom_mr, true);
+    }
     memory_region_add_subregion_overlap(rom_memory,
                                         PC_ROM_MIN_VGA,
                                         option_rom_mr,