diff --git a/clang/include/clang/Basic/FileManager.h b/clang/include/clang/Basic/FileManager.h
--- a/clang/include/clang/Basic/FileManager.h
+++ b/clang/include/clang/Basic/FileManager.h
@@ -243,6 +243,10 @@
   const FileSystemOptions &getFileSystemOpts() const { return FileSystemOpts; }
 
   llvm::vfs::FileSystem &getVirtualFileSystem() const { return *FS; }
+  llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>
+  getVirtualFileSystemPtr() const {
+    return FS;
+  }
 
   void setVirtualFileSystem(IntrusiveRefCntPtr<llvm::vfs::FileSystem> FS) {
     this->FS = std::move(FS);
diff --git a/clang/include/clang/Frontend/CompilerInvocation.h b/clang/include/clang/Frontend/CompilerInvocation.h
--- a/clang/include/clang/Frontend/CompilerInvocation.h
+++ b/clang/include/clang/Frontend/CompilerInvocation.h
@@ -294,6 +294,11 @@
     const CompilerInvocation &CI, DiagnosticsEngine &Diags,
     IntrusiveRefCntPtr<llvm::vfs::FileSystem> BaseFS);
 
+IntrusiveRefCntPtr<llvm::vfs::FileSystem>
+createVFSFromOverlayFiles(ArrayRef<std::string> VFSOverlayFiles,
+                          DiagnosticsEngine &Diags,
+                          IntrusiveRefCntPtr<llvm::vfs::FileSystem> BaseFS);
+
 } // namespace clang
 
 #endif // LLVM_CLANG_FRONTEND_COMPILERINVOCATION_H
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
@@ -551,6 +551,11 @@
                                StringRef SpecificModuleCachePath,
                                bool Complain) override {
     this->HSOpts = HSOpts;
+
+    this->PP.getFileManager().setVirtualFileSystem(createVFSFromOverlayFiles(
+        this->HSOpts.VFSOverlayFiles, this->PP.getDiagnostics(),
+        this->PP.getFileManager().getVirtualFileSystemPtr()));
+
     return false;
   }
 
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -4711,12 +4711,19 @@
 clang::createVFSFromCompilerInvocation(
     const CompilerInvocation &CI, DiagnosticsEngine &Diags,
     IntrusiveRefCntPtr<llvm::vfs::FileSystem> BaseFS) {
-  if (CI.getHeaderSearchOpts().VFSOverlayFiles.empty())
+  return createVFSFromOverlayFiles(CI.getHeaderSearchOpts().VFSOverlayFiles,
+                                   Diags, std::move(BaseFS));
+}
+
+IntrusiveRefCntPtr<llvm::vfs::FileSystem> clang::createVFSFromOverlayFiles(
+    ArrayRef<std::string> VFSOverlayFiles, DiagnosticsEngine &Diags,
+    IntrusiveRefCntPtr<llvm::vfs::FileSystem> BaseFS) {
+  if (VFSOverlayFiles.empty())
     return BaseFS;
 
   IntrusiveRefCntPtr<llvm::vfs::FileSystem> Result = BaseFS;
   // earlier vfs files are on the bottom
-  for (const auto &File : CI.getHeaderSearchOpts().VFSOverlayFiles) {
+  for (const auto &File : VFSOverlayFiles) {
     llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> Buffer =
         Result->getBufferForFile(File);
     if (!Buffer) {
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -5870,6 +5870,12 @@
     HSOpts.SystemHeaderPrefixes.emplace_back(std::move(Prefix), IsSystemHeader);
   }
 
+  // VFS overlay files.
+  for (unsigned N = Record[Idx++]; N; --N) {
+    std::string VFSOverlayFile = ReadString(Record, Idx);
+    HSOpts.VFSOverlayFiles.emplace_back(std::move(VFSOverlayFile));
+  }
+
   HSOpts.ResourceDir = ReadString(Record, Idx);
   HSOpts.ModuleCachePath = ReadString(Record, Idx);
   HSOpts.ModuleUserBuildPath = ReadString(Record, Idx);
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -1410,6 +1410,11 @@
     Record.push_back(HSOpts.SystemHeaderPrefixes[I].IsSystemHeader);
   }
 
+  // VFS overlay files.
+  Record.push_back(HSOpts.VFSOverlayFiles.size());
+  for (StringRef VFSOverlayFile : HSOpts.VFSOverlayFiles)
+    AddString(VFSOverlayFile, Record);
+
   AddString(HSOpts.ResourceDir, Record);
   AddString(HSOpts.ModuleCachePath, Record);
   AddString(HSOpts.ModuleUserBuildPath, Record);