diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 1bad8d8..4dd1d20 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -521,6 +521,12 @@
   Opts.PrepareForLTO = Args.hasArg(OPT_flto, OPT_flto_EQ);
   const Arg *A = Args.getLastArg(OPT_flto, OPT_flto_EQ);
   Opts.EmitFunctionSummary = A && A->containsValue("thin");
+  if (Arg *A = Args.getLastArg(OPT_fthinlto_index_EQ)) {
+    if (IK != IK_LLVM_IR)
+      Diags.Report(diag::err_drv_argument_only_allowed_with)
+          << A->getAsString(Args) << "-x ir";
+    Opts.ThinLTOIndexFile = Args.getLastArgValue(OPT_fthinlto_index_EQ);
+  }
 
   Opts.MSVolatile = Args.hasArg(OPT_fms_volatile);