diff --git a/src/include/cpu/x86/mtrr.h b/src/include/cpu/x86/mtrr.h
index 42964b02ea..6e30199c5f 100644
--- a/src/include/cpu/x86/mtrr.h
+++ b/src/include/cpu/x86/mtrr.h
@@ -30,6 +30,7 @@
 
 #define IA32_SMRR_PHYS_BASE		0x1f2
 #define IA32_SMRR_PHYS_MASK		0x1f3
+#define SMRR_PHYS_MASK_LOCK		(1 << 10)
 
 /* Specific to model_6fx and model_1067x */
 #define MSR_SMRR_PHYS_BASE		0xa0