diff --git a/MdePkg/Include/Library/BaseLib.h b/MdePkg/Include/Library/BaseLib.h
index 6998171bd5..213bc0c0e1 100644
--- a/MdePkg/Include/Library/BaseLib.h
+++ b/MdePkg/Include/Library/BaseLib.h
@@ -4932,6 +4932,28 @@ typedef union {
   UINTN     UintN;
 } IA32_CR4;
 
+///
+/// Byte packed structure for a segment descriptor in a GDT/LDT.
+///
+typedef union {
+  struct {
+    UINT32  LimitLow:16;
+    UINT32  BaseLow:16;
+    UINT32  BaseMid:8;
+    UINT32  Type:4;
+    UINT32  S:1;
+    UINT32  DPL:2;
+    UINT32  P:1;
+    UINT32  LimitHigh:4;
+    UINT32  AVL:1;
+    UINT32  L:1;
+    UINT32  DB:1;
+    UINT32  G:1;
+    UINT32  BaseHigh:8;
+  } Bits;
+  UINT64  Uint64;
+} IA32_SEGMENT_DESCRIPTOR;
+
 ///
 /// Byte packed structure for an IDTR, GDTR, LDTR descriptor.
 ///
diff --git a/MdePkg/Library/BaseLib/X86Thunk.c b/MdePkg/Library/BaseLib/X86Thunk.c
index 014287b3c2..ae223b3163 100644
--- a/MdePkg/Library/BaseLib/X86Thunk.c
+++ b/MdePkg/Library/BaseLib/X86Thunk.c
@@ -1,7 +1,7 @@
 /** @file
   Real Mode Thunk Functions for IA32 and x64.
 
-  Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2006 - 2011, 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
@@ -15,29 +15,6 @@
 
 #include "BaseLibInternals.h"
 
-
-//
-// Byte packed structure for a segment descriptor in a GDT/LDT
-//
-typedef union {
-  struct {
-    UINT32  LimitLow:16;
-    UINT32  BaseLow:16;
-    UINT32  BaseMid:8;
-    UINT32  Type:4;
-    UINT32  S:1;
-    UINT32  DPL:2;
-    UINT32  P:1;
-    UINT32  LimitHigh:4;
-    UINT32  AVL:1;
-    UINT32  L:1;
-    UINT32  DB:1;
-    UINT32  G:1;
-    UINT32  BaseHigh:8;
-  } Bits;
-  UINT64  Uint64;
-} IA32_SEGMENT_DESCRIPTOR;
-
 extern CONST UINT8                  m16Start;
 extern CONST UINT16                 m16Size;
 extern CONST UINT16                 mThunk16Attr;