diff --git a/clang/lib/Frontend/FrontendAction.cpp b/clang/lib/Frontend/FrontendAction.cpp
index 72377d8..6cfa121 100644
--- a/clang/lib/Frontend/FrontendAction.cpp
+++ b/clang/lib/Frontend/FrontendAction.cpp
@@ -211,6 +211,32 @@
     return true;
   }
 
+  if (!CI.getHeaderSearchOpts().VFSOverlayFiles.empty()) {
+    IntrusiveRefCntPtr<vfs::OverlayFileSystem>
+        Overlay(new vfs::OverlayFileSystem(vfs::getRealFileSystem()));
+    // earlier vfs files are on the bottom
+    const std::vector<std::string> &Files =
+        CI.getHeaderSearchOpts().VFSOverlayFiles;
+    for (std::vector<std::string>::const_iterator I = Files.begin(),
+                                                  E = Files.end();
+         I != E; ++I) {
+      OwningPtr<llvm::MemoryBuffer> Buffer;
+      if (llvm::errc::success != llvm::MemoryBuffer::getFile(*I, Buffer)) {
+        CI.getDiagnostics().Report(diag::err_missing_vfs_overlay_file) << *I;
+        goto failure;
+      }
+
+      IntrusiveRefCntPtr<vfs::FileSystem> FS =
+          vfs::getVFSFromYAML(Buffer.take(), /*DiagHandler*/0);
+      if (!FS.getPtr()) {
+        CI.getDiagnostics().Report(diag::err_invalid_vfs_overlay) << *I;
+        goto failure;
+      }
+      Overlay->pushOverlay(FS);
+    }
+    CI.setVirtualFileSystem(Overlay);
+  }
+
   // Set up the file and source managers, if needed.
   if (!CI.hasFileManager())
     CI.createFileManager();