diff --git a/clang/include/clang/Frontend/ASTUnit.h b/clang/include/clang/Frontend/ASTUnit.h
--- a/clang/include/clang/Frontend/ASTUnit.h
+++ b/clang/include/clang/Frontend/ASTUnit.h
@@ -688,17 +688,25 @@
   /// lifetime is expected to extend past that of the returned ASTUnit.
   ///
   /// \returns - The initialized ASTUnit or null if the AST failed to load.
-  static std::unique_ptr<ASTUnit>
-  LoadFromASTFile(const std::string &Filename,
-                  const PCHContainerReader &PCHContainerRdr, WhatToLoad ToLoad,
-                  IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
-                  const FileSystemOptions &FileSystemOpts,
-                  bool UseDebugInfo = false, bool OnlyLocalDecls = false,
-                  CaptureDiagsKind CaptureDiagnostics = CaptureDiagsKind::None,
-                  bool AllowASTWithCompilerErrors = false,
-                  bool UserFilesAreVolatile = false);
+  static std::unique_ptr<ASTUnit> LoadFromASTFile(
+      const std::string &Filename, const PCHContainerReader &PCHContainerRdr,
+      WhatToLoad ToLoad, IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
+      IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
+      const FileSystemOptions &FileSystemOpts, bool UseDebugInfo = false,
+      bool OnlyLocalDecls = false,
+      CaptureDiagsKind CaptureDiagnostics = CaptureDiagsKind::None,
+      bool AllowASTWithCompilerErrors = false,
+      bool UserFilesAreVolatile = false);
+  static std::unique_ptr<ASTUnit> LoadFromASTFile(
+      const std::string &Filename, const PCHContainerReader &PCHContainerRdr,
+      WhatToLoad ToLoad, IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
+      const FileSystemOptions &FileSystemOpts, bool UseDebugInfo = false,
+      bool OnlyLocalDecls = false,
+      CaptureDiagsKind CaptureDiagnostics = CaptureDiagsKind::None,
+      bool AllowASTWithCompilerErrors = false,
+      bool UserFilesAreVolatile = false);
 
-private:
+ private:
   /// Helper function for \c LoadFromCompilerInvocation() and
   /// \c LoadFromCommandLine(), which loads an AST from a compiler invocation.
   ///
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -757,6 +757,7 @@
 std::unique_ptr<ASTUnit> ASTUnit::LoadFromASTFile(
     const std::string &Filename, const PCHContainerReader &PCHContainerRdr,
     WhatToLoad ToLoad, IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
+    IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
     const FileSystemOptions &FileSystemOpts, bool UseDebugInfo,
     bool OnlyLocalDecls, CaptureDiagsKind CaptureDiagnostics,
     bool AllowASTWithCompilerErrors, bool UserFilesAreVolatile) {
@@ -775,8 +776,6 @@
   AST->OnlyLocalDecls = OnlyLocalDecls;
   AST->CaptureDiagnostics = CaptureDiagnostics;
   AST->Diagnostics = Diags;
-  IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS =
-      llvm::vfs::getRealFileSystem();
   AST->FileMgr = new FileManager(FileSystemOpts, VFS);
   AST->UserFilesAreVolatile = UserFilesAreVolatile;
   AST->SourceMgr = new SourceManager(AST->getDiagnostics(),
@@ -867,6 +866,18 @@
   return AST;
 }
 
+std::unique_ptr<ASTUnit> ASTUnit::LoadFromASTFile(
+    const std::string &Filename, const PCHContainerReader &PCHContainerRdr,
+    WhatToLoad ToLoad, IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
+    const FileSystemOptions &FileSystemOpts, bool UseDebugInfo,
+    bool OnlyLocalDecls, CaptureDiagsKind CaptureDiagnostics,
+    bool AllowASTWithCompilerErrors, bool UserFilesAreVolatile) {
+  return LoadFromASTFile(Filename, PCHContainerRdr, ToLoad, Diags,
+                         llvm::vfs::getRealFileSystem(), FileSystemOpts,
+                         UseDebugInfo, OnlyLocalDecls, CaptureDiagnostics,
+                         AllowASTWithCompilerErrors, UserFilesAreVolatile);
+}
+
 /// Add the given macro to the hash of all top-level entities.
 static void AddDefinedMacroToHash(const Token &MacroNameTok, unsigned &Hash) {
   Hash = llvm::djbHash(MacroNameTok.getIdentifierInfo()->getName(), Hash);