diff --git a/OvmfPkg/XenBusDxe/X64/TestAndClearBit.nasm b/OvmfPkg/XenBusDxe/X64/TestAndClearBit.nasm
index 38ac5490cb..a4859a62a2 100644
--- a/OvmfPkg/XenBusDxe/X64/TestAndClearBit.nasm
+++ b/OvmfPkg/XenBusDxe/X64/TestAndClearBit.nasm
@@ -9,8 +9,7 @@ SECTION .text
 ;   );
 global ASM_PFX(TestAndClearBit)
 ASM_PFX(TestAndClearBit):
-  lock
-  btr [rdx], ecx
+  lock btr [rdx], ecx
   sbb eax, eax
   ret