diff --git a/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/Ia32/Thunk16.S b/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/Ia32/Thunk16.S
index 6055ca663c..b33d67c9ed 100644
--- a/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/Ia32/Thunk16.S
+++ b/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/Ia32/Thunk16.S
@@ -1,6 +1,6 @@
 #------------------------------------------------------------------------------
 #
-# Copyright (c) 2006 - 2010, 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
@@ -55,7 +55,8 @@ ASM_PFX(ThunkAttr): .space  4
     orb     $2, %al
     outb    %al, $0x92                  # deactivate A20M#
 2:
-    movw    %ss, %ax
+    xorw    %ax, %ax                    # xor eax, eax 
+    movl    %ss, %eax                   # mov ax, ss
     .byte   0x67, 0x66, 0x8d, 0x6c, 0x24, 0x34, 0x66
     mov     %ebp, 0xffffffd8(%esi)
     mov     0xfffffff8(%esi), %ebx
diff --git a/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/Ia32/Thunk16.asm b/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/Ia32/Thunk16.asm
index 61508d73bc..8b22e0f336 100644
--- a/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/Ia32/Thunk16.asm
+++ b/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/Ia32/Thunk16.asm
@@ -1,4 +1,4 @@
-; Copyright (c) 2004 - 2010, Intel Corporation. All rights reserved.<BR>
+; Copyright (c) 2004 - 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        
@@ -108,7 +108,8 @@ _ThunkAttr  DD      ?
     or      al, 2
     out     92h, al                     ; deactivate A20M#
 @2:
-    mov     ax, ss
+    xor     ax, ax                      ; xor eax, eax
+    mov     eax, ss                     ; mov ax, ss
     DB      67h
     lea     bp, [esp + sizeof (IA32_REGS)]
     ;
diff --git a/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/X64/Thunk16.S b/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/X64/Thunk16.S
index 1de788a184..038cc75a67 100644
--- a/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/X64/Thunk16.S
+++ b/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/X64/Thunk16.S
@@ -1,6 +1,6 @@
 #------------------------------------------------------------------------------
 #
-# Copyright (c) 2006 - 2010, 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
@@ -109,7 +109,8 @@ L_1:
     orb     $2,%al
     outb    %al, $0x92                   # deactivate A20M#
 L_2: 
-    movw    %ss,%ax
+    xorw    %ax,%ax                      # xor eax, eax
+    movl    %ss,%eax                     # mov ax, ss
     lea     IA32_REGS_SIZE(%esp), %bp
     #
     # rsi in the following 2 instructions is indeed bp in 16-bit code
diff --git a/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/X64/Thunk16.asm b/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/X64/Thunk16.asm
index c7d9caefe7..b181a4ccfd 100644
--- a/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/X64/Thunk16.asm
+++ b/EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/X64/Thunk16.asm
@@ -1,4 +1,4 @@
-; Copyright (c) 2004 - 2010, Intel Corporation. All rights reserved.<BR>
+; Copyright (c) 2004 - 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        
@@ -103,7 +103,8 @@ _ThunkAttr  DD      ?
     or      al, 2
     out     92h, al                     ; deactivate A20M#
 @2:
-    mov     ax, ss
+    xor     ax, ax                      ; xor eax, eax
+    mov     eax, ss                     ; mov ax, ss
     lea     bp, [esp + sizeof (IA32_REGS)]
     ;
     ; rsi in the following 2 instructions is indeed bp in 16-bit code
diff --git a/EdkCompatibilityPkg/Foundation/Library/Thunk16/Ia32/Thunk16.S b/EdkCompatibilityPkg/Foundation/Library/Thunk16/Ia32/Thunk16.S
index 55415d8703..cf7776a6a3 100644
--- a/EdkCompatibilityPkg/Foundation/Library/Thunk16/Ia32/Thunk16.S
+++ b/EdkCompatibilityPkg/Foundation/Library/Thunk16/Ia32/Thunk16.S
@@ -1,6 +1,6 @@
 #*****************************************************************************
 #*
-#*   Copyright (c) 2006 - 2010, 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        
@@ -116,7 +116,8 @@ L_16Bit:
     .byte  0xfc
     
 L_Lable1:
-    movl   %ss,%eax
+    xor    %eax,%eax
+    movw   %ss,%ax
     shl    $0x4,%eax
     add    %esp,%eax
     lss    0x3c(%esp),%esp
diff --git a/EdkCompatibilityPkg/Foundation/Library/Thunk16/Ia32/Thunk16.asm b/EdkCompatibilityPkg/Foundation/Library/Thunk16/Ia32/Thunk16.asm
index 76c1317469..0a796ed236 100644
--- a/EdkCompatibilityPkg/Foundation/Library/Thunk16/Ia32/Thunk16.asm
+++ b/EdkCompatibilityPkg/Foundation/Library/Thunk16/Ia32/Thunk16.asm
@@ -1,6 +1,6 @@
 ;*****************************************************************************
 ;*
-;*   Copyright (c) 2006 - 2010, 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        
@@ -141,7 +141,8 @@ __Thunk16   PROC    USES    ebp ebx esi edi ds  es  fs  gs
     mov     cr4, eax                    ; disable PAE & PSE
     db      67h, 0FFh, 06Ch, 024h, 0FCh ; jmp     dword ptr [esp-4]
 @@:
-    mov     eax, ss
+    xor     eax, eax
+    mov     ax, ss
     shl     eax, 4
     add     eax, esp                    ; eax <- address of 16-bit stack
     lss     esp, fword ptr (_STK16 ptr [esp + sizeof (IA32_REGS)]).SavedEsp
diff --git a/EdkCompatibilityPkg/Foundation/Library/Thunk16/X64/Thunk16.S b/EdkCompatibilityPkg/Foundation/Library/Thunk16/X64/Thunk16.S
index 7328ab764d..f77388d811 100644
--- a/EdkCompatibilityPkg/Foundation/Library/Thunk16/X64/Thunk16.S
+++ b/EdkCompatibilityPkg/Foundation/Library/Thunk16/X64/Thunk16.S
@@ -148,7 +148,7 @@ Label_16Bit:
 
 Label:
       xor    %rax,%rax
-      movl   %ss,%eax
+      movw   %ss,%ax
       shl    $0x4,%eax
       add    %esp,%eax
       mov    %r15,%rsp
diff --git a/EdkCompatibilityPkg/Foundation/Library/Thunk16/X64/Thunk16.asm b/EdkCompatibilityPkg/Foundation/Library/Thunk16/X64/Thunk16.asm
index 0638d5faa8..6b74bbe7cb 100644
--- a/EdkCompatibilityPkg/Foundation/Library/Thunk16/X64/Thunk16.asm
+++ b/EdkCompatibilityPkg/Foundation/Library/Thunk16/X64/Thunk16.asm
@@ -144,7 +144,7 @@ _Thunk16    PROC    USES    rbp rbx rsi rdi r12 r13 r14 r15
     retf
 @@:
     xor     rax, rax
-    mov     eax, ss
+    mov     ax, ss
     shl     eax, 4
     add     eax, esp                    ; rax <- address of 16-bit stack
     mov     rsp, r15