diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index 1fb161a..efd1917 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -484,6 +484,11 @@
   if (Args.hasArg(options::OPT__relocatable_pch, true))
     CmdArgs.push_back("--relocatable-pch");
                       
+   if (Arg *A = Args.getLastArg(options::OPT_fconstant_string_class_EQ)) {
+     CmdArgs.push_back("-fconstant-string-class");
+     CmdArgs.push_back(A->getValue(Args));
+   }
+
   // Forward -f options which we can pass directly.
   Args.AddLastArg(CmdArgs, options::OPT_femit_all_decls);
   Args.AddLastArg(CmdArgs, options::OPT_ffreestanding);