diff --git a/OvmfPkg/XenBusDxe/X64/TestAndClearBit.S b/OvmfPkg/XenBusDxe/X64/TestAndClearBit.S
deleted file mode 100644
index 0372e83bdd..0000000000
--- a/OvmfPkg/XenBusDxe/X64/TestAndClearBit.S
+++ /dev/null
@@ -1,12 +0,0 @@
-# INT32
-# EFIAPI
-# TestAndClearBit (
-#   IN  INT32 Bit,                // rcx
-#   IN  volatile VOID* Address    // rdx
-#   );
-ASM_GLOBAL ASM_PFX(TestAndClearBit)
-ASM_PFX(TestAndClearBit):
-  lock
-  btrl %ecx, (%rdx)
-  sbbl %eax, %eax
-  ret
diff --git a/OvmfPkg/XenBusDxe/X64/TestAndClearBit.asm b/OvmfPkg/XenBusDxe/X64/TestAndClearBit.nasm
similarity index 63%
rename from OvmfPkg/XenBusDxe/X64/TestAndClearBit.asm
rename to OvmfPkg/XenBusDxe/X64/TestAndClearBit.nasm
index 3a2587913e..38ac5490cb 100644
--- a/OvmfPkg/XenBusDxe/X64/TestAndClearBit.asm
+++ b/OvmfPkg/XenBusDxe/X64/TestAndClearBit.nasm
@@ -1,4 +1,5 @@
-.code
+DEFAULT REL
+SECTION .text
 
 ; INT32
 ; EFIAPI
@@ -6,11 +7,10 @@
 ;   IN  INT32 Bit,                // rcx
 ;   IN  volatile VOID* Address    // rdx
 ;   );
-TestAndClearBit PROC
+global ASM_PFX(TestAndClearBit)
+ASM_PFX(TestAndClearBit):
   lock
   btr [rdx], ecx
   sbb eax, eax
   ret
-TestAndClearBit ENDP
 
-END
diff --git a/OvmfPkg/XenBusDxe/XenBusDxe.inf b/OvmfPkg/XenBusDxe/XenBusDxe.inf
index 61f7568e55..4ce4743454 100644
--- a/OvmfPkg/XenBusDxe/XenBusDxe.inf
+++ b/OvmfPkg/XenBusDxe/XenBusDxe.inf
@@ -56,8 +56,7 @@
 [Sources.X64]
   X64/hypercall.nasm
   X64/InterlockedCompareExchange16.nasm
-  X64/TestAndClearBit.S
-  X64/TestAndClearBit.asm
+  X64/TestAndClearBit.nasm
 
 [LibraryClasses]
   UefiDriverEntryPoint