diff --git a/llvm/lib/Target/X86/X86ExpandPseudo.cpp b/llvm/lib/Target/X86/X86ExpandPseudo.cpp
index d9c0964e9ed834..b1d15225eaaf1f 100644
--- a/llvm/lib/Target/X86/X86ExpandPseudo.cpp
+++ b/llvm/lib/Target/X86/X86ExpandPseudo.cpp
@@ -346,7 +346,9 @@ bool X86ExpandPseudo::ExpandMI(MachineBasicBlock &MBB,
 
     // Copy the input argument of the pseudo into the argument of the
     // actual instruction.
-    TII->copyPhysReg(MBB, MBBI, DL, X86::RBX, InArg.getReg(), InArg.isKill());
+    // NOTE: We don't copy the kill flag since the input might be the same reg
+    // as one of the other operands of LCMPXCHG16B.
+    TII->copyPhysReg(MBB, MBBI, DL, X86::RBX, InArg.getReg(), false);
     // Create the actual instruction.
     MachineInstr *NewInstr = BuildMI(MBB, MBBI, DL, TII->get(X86::LCMPXCHG16B));
     // Copy the operands related to the address.
diff --git a/llvm/test/CodeGen/X86/pr42064.ll b/llvm/test/CodeGen/X86/pr42064.ll
index 6269a59ff055e6..089895da18a1df 100644
--- a/llvm/test/CodeGen/X86/pr42064.ll
+++ b/llvm/test/CodeGen/X86/pr42064.ll
@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
-; RUN: llc < %s -mtriple=x86_64-pc-windows-msvc19.11.0 -mattr=+avx,+cx16 | FileCheck %s
+; RUN: llc < %s -verify-machineinstrs -mtriple=x86_64-pc-windows-msvc19.11.0 -mattr=+avx,+cx16 | FileCheck %s
 
 %struct.TestStruct = type { %union.Int128 }
 %union.Int128 = type { i128 }