diff --git a/MdePkg/Include/Uefi/UefiMultiPhase.h b/MdePkg/Include/Uefi/UefiMultiPhase.h
index 7884913371..1f1f3f45e5 100644
--- a/MdePkg/Include/Uefi/UefiMultiPhase.h
+++ b/MdePkg/Include/Uefi/UefiMultiPhase.h
@@ -108,7 +108,22 @@ typedef enum {
   /// by a corresponding call to the underlying isolation architecture.
   ///
   EfiUnacceptedMemoryType,
-  EfiMaxMemoryType
+  EfiMaxMemoryType,
+  //
+  // +---------------------------------------------------+
+  // | 0..(EfiMaxMemoryType - 1)    - Normal memory type |
+  // +---------------------------------------------------+
+  // | EfiMaxMemoryType..0x6FFFFFFF - Invalid            |
+  // +---------------------------------------------------+
+  // | 0x70000000..0x7FFFFFFF       - OEM reserved       |
+  // +---------------------------------------------------+
+  // | 0x80000000..0xFFFFFFFF       - OS reserved        |
+  // +---------------------------------------------------+
+  //
+  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;
 
 ///