diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index 4392f4f..3e1eb88 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -55,9 +55,7 @@
     else
       CmdArgs.push_back("-E");
   } else if (isa<PrecompileJobAction>(JA)) {
-    // No special option needed, driven by -x.
-    //
-    // FIXME: Don't drive this by -x, that is gross.
+    CmdArgs.push_back("-emit-pth");
   } else {
     assert(isa<CompileJobAction>(JA) && "Invalid action for clang tool.");