diff --git a/MdePkg/Library/BaseMemoryLibOptDxe/BaseMemoryLibOptDxe.inf b/MdePkg/Library/BaseMemoryLibOptDxe/BaseMemoryLibOptDxe.inf
index e8268bf..999f4e8 100644
--- a/MdePkg/Library/BaseMemoryLibOptDxe/BaseMemoryLibOptDxe.inf
+++ b/MdePkg/Library/BaseMemoryLibOptDxe/BaseMemoryLibOptDxe.inf
@@ -110,6 +110,7 @@
   X64/ZeroMem.nasm
   X64/ZeroMem.asm
   X64/ZeroMem.S
+  X64/SetMem64.nasm
   X64/SetMem64.asm
   X64/SetMem64.S
   X64/SetMem32.asm
diff --git a/MdePkg/Library/BaseMemoryLibOptDxe/X64/SetMem64.nasm b/MdePkg/Library/BaseMemoryLibOptDxe/X64/SetMem64.nasm
new file mode 100644
index 0000000..d047158
--- /dev/null
+++ b/MdePkg/Library/BaseMemoryLibOptDxe/X64/SetMem64.nasm
@@ -0,0 +1,46 @@
+;------------------------------------------------------------------------------
+;
+; Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>
+; This program and the accompanying materials
+; are licensed and made available under the terms and conditions of the BSD License
+; which accompanies this distribution.  The full text of the license may be found at
+; http://opensource.org/licenses/bsd-license.php.
+;
+; THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+; WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+;
+; Module Name:
+;
+;   SetMem64.Asm
+;
+; Abstract:
+;
+;   SetMem64 function
+;
+; Notes:
+;
+;------------------------------------------------------------------------------
+
+    DEFAULT REL
+    SECTION .text
+
+;------------------------------------------------------------------------------
+;  VOID *
+;  InternalMemSetMem64 (
+;    IN VOID   *Buffer,
+;    IN UINTN  Count,
+;    IN UINT64 Value
+;    )
+;------------------------------------------------------------------------------
+global ASM_PFX(InternalMemSetMem64)
+ASM_PFX(InternalMemSetMem64):
+    push    rdi
+    push    rcx
+    mov     rdi, rcx
+    mov     rax, r8
+    xchg    rcx, rdx
+    rep     stosq
+    pop     rax
+    pop     rdi
+    ret
+