diff --git a/MdePkg/Include/Uefi/UefiSpec.h b/MdePkg/Include/Uefi/UefiSpec.h
index e83e14d347..5de00e8ea2 100644
--- a/MdePkg/Include/Uefi/UefiSpec.h
+++ b/MdePkg/Include/Uefi/UefiSpec.h
@@ -110,6 +110,21 @@ typedef enum {
 //
 #define EFI_MEMORY_RUNTIME  0x8000000000000000ULL
 
+//
+// If this flag is set, the memory region is
+// described with additional ISA-specific memory attributes
+// as specified in EFI_MEMORY_ISA_MASK.
+//
+#define EFI_MEMORY_ISA_VALID  0x4000000000000000ULL
+
+//
+// Defines the bits reserved for describing optional ISA-specific cacheability
+// attributes that are not covered by the standard UEFI Memory Attributes cacheability
+// bits (EFI_MEMORY_UC, EFI_MEMORY_WC, EFI_MEMORY_WT, EFI_MEMORY_WB and EFI_MEMORY_UCE).
+// See Calling Conventions for further ISA-specific enumeration of these bits.
+//
+#define EFI_MEMORY_ISA_MASK  0x0FFFF00000000000ULL
+
 //
 // Attributes bitmasks, grouped by type
 //