diff --git a/build_opts/X86_FS b/build_opts/X86_FS
index 72cba7443a..ddec6186d8 100644
--- a/build_opts/X86_FS
+++ b/build_opts/X86_FS
@@ -1,4 +1,4 @@
 TARGET_ISA = 'x86'
-CPU_MODELS = 'AtomicSimpleCPU,TimingSimpleCPU'
+CPU_MODELS = 'AtomicSimpleCPU,O3CPU,TimingSimpleCPU'
 FULL_SYSTEM = 1
 PROTOCOL = 'MI_example'