diff --git a/BaseTools/Source/C/Include/Common/UefiMultiPhase.h b/BaseTools/Source/C/Include/Common/UefiMultiPhase.h
index b889508b85..5b5af8b43c 100644
--- a/BaseTools/Source/C/Include/Common/UefiMultiPhase.h
+++ b/BaseTools/Source/C/Include/Common/UefiMultiPhase.h
@@ -14,6 +14,15 @@
 
 //
 // Enumeration of memory types introduced in UEFI.
+// +---------------------------------------------------+
+// | 0..(EfiMaxMemoryType - 1)    - Normal memory type |
+// +---------------------------------------------------+
+// | EfiMaxMemoryType..0x6FFFFFFF - Invalid            |
+// +---------------------------------------------------+
+// | 0x70000000..0x7FFFFFFF       - OEM reserved       |
+// +---------------------------------------------------+
+// | 0x80000000..0xFFFFFFFF       - OS reserved        |
+// +---------------------------------------------------+
 //
 typedef enum {
   EfiReservedMemoryType,
@@ -31,7 +40,11 @@ typedef enum {
   EfiMemoryMappedIOPortSpace,
   EfiPalCode,
   EfiPersistentMemory,
-  EfiMaxMemoryType
+  EfiMaxMemoryType,
+  MEMORY_TYPE_OEM_RESERVED_MIN = 0x70000000,
+  MEMORY_TYPE_OEM_RESERVED_MAX = 0x7FFFFFFF,
+  MEMORY_TYPE_OS_RESERVED_MIN  = 0x80000000,
+  MEMORY_TYPE_OS_RESERVED_MAX  = 0xFFFFFFFF
 } EFI_MEMORY_TYPE;