diff --git a/MdePkg/Library/BaseSynchronizationLib/Ia32/InterlockedCompareExchange64.nasm b/MdePkg/Library/BaseSynchronizationLib/Ia32/InterlockedCompareExchange64.nasm
index ee63ff7f12..206de407ae 100644
--- a/MdePkg/Library/BaseSynchronizationLib/Ia32/InterlockedCompareExchange64.nasm
+++ b/MdePkg/Library/BaseSynchronizationLib/Ia32/InterlockedCompareExchange64.nasm
@@ -41,7 +41,7 @@ ASM_PFX(InternalSyncCompareExchange64):
     mov     edx, [esp + 20]
     mov     ebx, [esp + 24]
     mov     ecx, [esp + 28]
-    lock    cmpxchg8b   qword [esi]
+    lock    cmpxchg8b [esi]
     pop     ebx
     pop     esi
     ret