diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -6170,7 +6170,13 @@
   Args.AddLastArg(CmdArgs, options::OPT_fvisibility_inlines_hidden_static_local_var,
                            options::OPT_fno_visibility_inlines_hidden_static_local_var);
   Args.AddLastArg(CmdArgs, options::OPT_fvisibility_global_new_delete_hidden);
-  Args.AddLastArg(CmdArgs, options::OPT_ftlsmodel_EQ);
+  if (Triple.isOSSerenity()) {
+    StringRef tls_model =
+        Args.getLastArgValue(options::OPT_ftlsmodel_EQ, "initial-exec");
+    CmdArgs.push_back(Args.MakeArgString("-ftls-model=" + tls_model));
+  } else {
+    Args.AddLastArg(CmdArgs, options::OPT_ftlsmodel_EQ);
+  }
 
   if (Args.hasFlag(options::OPT_fnew_infallible,
                    options::OPT_fno_new_infallible, false))