diff --git a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.inf b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.inf
index f163de3d3f..a95e1e730c 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.inf
+++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgLib.inf
@@ -39,8 +39,7 @@
   Ia32/IoLibExAsm.nasm
 
 [Sources.X64]
-  X64/IoLibExAsm.asm
-  X64/IoLibExAsm.S
+  X64/IoLibExAsm.nasm
 
 [Packages]
   MdePkg/MdePkg.dec
diff --git a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgSecLib.inf b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgSecLib.inf
index 5c5c5c7f40..03a659c9b0 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgSecLib.inf
+++ b/OvmfPkg/Library/QemuFwCfgLib/QemuFwCfgSecLib.inf
@@ -37,8 +37,7 @@
   Ia32/IoLibExAsm.nasm
 
 [Sources.X64]
-  X64/IoLibExAsm.asm
-  X64/IoLibExAsm.S
+  X64/IoLibExAsm.nasm
 
 [Packages]
   MdePkg/MdePkg.dec
diff --git a/OvmfPkg/Library/QemuFwCfgLib/X64/IoLibExAsm.S b/OvmfPkg/Library/QemuFwCfgLib/X64/IoLibExAsm.S
deleted file mode 100644
index 69167b7081..0000000000
--- a/OvmfPkg/Library/QemuFwCfgLib/X64/IoLibExAsm.S
+++ /dev/null
@@ -1,47 +0,0 @@
-#------------------------------------------------------------------------------
-#
-# Copyright (c) 2006 - 2013, 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.
-#
-#------------------------------------------------------------------------------
-
-#------------------------------------------------------------------------------
-#  VOID
-#  EFIAPI
-#  IoReadFifo8 (
-#    IN UINTN                  Port,              // rcx
-#    IN UINTN                  Size,              // rdx
-#    IN VOID                   *Buffer            // r8
-#    );
-#------------------------------------------------------------------------------
-ASM_GLOBAL ASM_PFX(IoReadFifo8)
-ASM_PFX(IoReadFifo8):
-    xchg    %rcx, %rdx
-    xchg    %r8, %rdi           # rdi: buffer address; r8: save rdi
-rep insb
-    mov     %r8, %rdi           # restore rdi
-    ret
-
-#------------------------------------------------------------------------------
-#  VOID
-#  EFIAPI
-#  IoWriteFifo8 (
-#    IN UINTN                  Port,              // rcx
-#    IN UINTN                  Size,              // rdx
-#    IN VOID                   *Buffer            // r8
-#    );
-#------------------------------------------------------------------------------
-ASM_GLOBAL ASM_PFX(IoWriteFifo8)
-ASM_PFX(IoWriteFifo8):
-    xchg    %rcx, %rdx
-    xchg    %r8, %rsi           # rdi: buffer address; r8: save rsi
-rep outsb
-    mov     %r8, %rsi           # restore rsi
-    ret
-
diff --git a/OvmfPkg/Library/QemuFwCfgLib/X64/IoLibExAsm.asm b/OvmfPkg/Library/QemuFwCfgLib/X64/IoLibExAsm.nasm
similarity index 90%
rename from OvmfPkg/Library/QemuFwCfgLib/X64/IoLibExAsm.asm
rename to OvmfPkg/Library/QemuFwCfgLib/X64/IoLibExAsm.nasm
index 47ac158f85..f1078f2088 100644
--- a/OvmfPkg/Library/QemuFwCfgLib/X64/IoLibExAsm.asm
+++ b/OvmfPkg/Library/QemuFwCfgLib/X64/IoLibExAsm.nasm
@@ -11,7 +11,8 @@
 ;
 ;------------------------------------------------------------------------------
 
-    .code
+    DEFAULT REL
+    SECTION .text
 
 ;------------------------------------------------------------------------------
 ;  VOID
@@ -22,7 +23,8 @@
 ;    IN VOID                   *Buffer            // r8
 ;    );
 ;------------------------------------------------------------------------------
-IoReadFifo8 PROC
+global ASM_PFX(IoReadFifo8)
+ASM_PFX(IoReadFifo8):
 
     xchg    rcx, rdx
     xchg    rdi, r8             ; rdi: buffer address; r8: save rdi
@@ -30,9 +32,6 @@ rep insb
     mov     rdi, r8             ; restore rdi
     ret
 
-IoReadFifo8 ENDP
-
-
 ;------------------------------------------------------------------------------
 ;  VOID
 ;  EFIAPI
@@ -42,7 +41,8 @@ IoReadFifo8 ENDP
 ;    IN VOID                   *Buffer            // r8
 ;    );
 ;------------------------------------------------------------------------------
-IoWriteFifo8 PROC
+global ASM_PFX(IoWriteFifo8)
+ASM_PFX(IoWriteFifo8):
 
     xchg    rcx, rdx
     xchg    rsi, r8             ; rdi: buffer address; r8: save rdi
@@ -50,7 +50,3 @@ rep outsb
     mov     rsi, r8             ; restore rdi
     ret
 
-IoWriteFifo8 ENDP
-
-    END
-