diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index d398904..45760ae 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -70,6 +70,15 @@
   Builder.append(Twine("#include \"") + File + "\"");
 }
 
+/// AddImplicitSystemIncludeIfExists - Add an implicit system \#include of the 
+/// specified file to the predefines buffer: precheck with __has_include.
+static void AddImplicitSystemIncludeIfExists(MacroBuilder &Builder, 
+                                             StringRef File) {
+  Builder.append(Twine("#if __has_include( <") + File + ">)");
+  Builder.append(Twine("#include <") + File + ">");
+  Builder.append(Twine("#endif"));
+}
+
 static void AddImplicitIncludeMacros(MacroBuilder &Builder, StringRef File) {
   Builder.append(Twine("#__include_macros \"") + File + "\"");
   // Marker token to stop the __include_macros fetch loop.
@@ -1133,6 +1142,13 @@
   if (!PP.getLangOpts().AsmPreprocessor)
     Builder.append("# 1 \"<built-in>\" 2");
 
+  // Process -fsystem-include-if-exists directives.
+  for (unsigned i = 0, 
+       e = InitOpts.FSystemIncludeIfExists.size(); i != e; ++i) {
+    const std::string &Path = InitOpts.FSystemIncludeIfExists[i];
+    AddImplicitSystemIncludeIfExists(Builder, Path);
+  }
+
   // If -imacros are specified, include them now.  These are processed before
   // any -include directives.
   for (unsigned i = 0, e = InitOpts.MacroIncludes.size(); i != e; ++i)