diff --git a/clang-tools-extra/clangd/ClangdLSPServer.cpp b/clang-tools-extra/clangd/ClangdLSPServer.cpp
--- a/clang-tools-extra/clangd/ClangdLSPServer.cpp
+++ b/clang-tools-extra/clangd/ClangdLSPServer.cpp
@@ -666,8 +666,9 @@
     log("Trying to incrementally change non-added document: {0}", File);
     return;
   }
+  std::string NewCode(*Code);
   for (const auto &Change : Params.contentChanges) {
-    if (auto Err = applyChange(*Code, Change)) {
+    if (auto Err = applyChange(NewCode, Change)) {
       // If this fails, we are most likely going to be not in sync anymore with
       // the client.  It is better to remove the draft and let further
       // operations fail rather than giving wrong results.
@@ -676,7 +677,7 @@
       return;
     }
   }
-  Server->addDocument(File, *Code, encodeVersion(Params.textDocument.version),
+  Server->addDocument(File, NewCode, encodeVersion(Params.textDocument.version),
                       WantDiags, Params.forceRebuild);
 }
 
diff --git a/clang-tools-extra/clangd/ClangdServer.h b/clang-tools-extra/clangd/ClangdServer.h
--- a/clang-tools-extra/clangd/ClangdServer.h
+++ b/clang-tools-extra/clangd/ClangdServer.h
@@ -339,7 +339,7 @@
   /// FIXME: those metrics might be useful too, we should add them.
   llvm::StringMap<TUScheduler::FileStats> fileStats() const;
 
-  llvm::Optional<std::string> getDraft(PathRef File) const;
+  std::shared_ptr<const std::string> getDraft(PathRef File) const;
 
   // Blocks the main thread until the server is idle. Only for use in tests.
   // Returns false if the timeout expires.
@@ -385,6 +385,25 @@
   // Only written from the main thread (despite being threadsafe).
   // FIXME: TUScheduler also keeps these, unify?
   DraftStore DraftMgr;
+
+  class DirtyFS : public ThreadsafeFS {
+  public:
+    DirtyFS(const ThreadsafeFS &Base, const DraftStore &Drafts)
+        : Base(Base), DirtyFiles(Drafts) {}
+
+  private:
+    llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> viewImpl() const override {
+      auto OFS = llvm::makeIntrusiveRefCnt<llvm::vfs::OverlayFileSystem>(
+          Base.view(llvm::None));
+      OFS->pushOverlay(DirtyFiles.asVFS());
+      return OFS;
+    }
+
+    const ThreadsafeFS &Base;
+    const DraftStore &DirtyFiles;
+  };
+
+  DirtyFS DirtyFS{TFS, DraftMgr};
 };
 
 } // namespace clangd
diff --git a/clang-tools-extra/clangd/ClangdServer.cpp b/clang-tools-extra/clangd/ClangdServer.cpp
--- a/clang-tools-extra/clangd/ClangdServer.cpp
+++ b/clang-tools-extra/clangd/ClangdServer.cpp
@@ -218,14 +218,14 @@
   for (const Path &FilePath : DraftMgr.getActiveFiles())
     if (Filter(FilePath))
       if (auto Draft = DraftMgr.getDraft(FilePath)) // else disappeared in race?
-        addDocument(FilePath, std::move(Draft->Contents), Draft->Version,
+        addDocument(FilePath, *Draft->Contents, Draft->Version,
                     WantDiagnostics::Auto);
 }
 
-llvm::Optional<std::string> ClangdServer::getDraft(PathRef File) const {
+std::shared_ptr<const std::string> ClangdServer::getDraft(PathRef File) const {
   auto Draft = DraftMgr.getDraft(File);
   if (!Draft)
-    return llvm::None;
+    return nullptr;
   return std::move(Draft->Contents);
 }
 
diff --git a/clang-tools-extra/clangd/DraftStore.h b/clang-tools-extra/clangd/DraftStore.h
--- a/clang-tools-extra/clangd/DraftStore.h
+++ b/clang-tools-extra/clangd/DraftStore.h
@@ -13,6 +13,7 @@
 #include "support/Path.h"
 #include "clang/Basic/LLVM.h"
 #include "llvm/ADT/StringMap.h"
+#include "llvm/Support/VirtualFileSystem.h"
 #include <mutex>
 #include <string>
 #include <vector>
@@ -27,7 +28,7 @@
 class DraftStore {
 public:
   struct Draft {
-    std::string Contents;
+    std::shared_ptr<const std::string> Contents;
     std::string Version;
   };
 
@@ -47,9 +48,15 @@
   /// Remove the draft from the store.
   void removeDraft(PathRef File);
 
+  llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> asVFS() const;
+
 private:
+  struct DraftAndTime {
+    Draft Draft;
+    time_t MTime;
+  };
   mutable std::mutex Mutex;
-  llvm::StringMap<Draft> Drafts;
+  llvm::StringMap<DraftAndTime> Drafts;
 };
 
 } // namespace clangd
diff --git a/clang-tools-extra/clangd/DraftStore.cpp b/clang-tools-extra/clangd/DraftStore.cpp
--- a/clang-tools-extra/clangd/DraftStore.cpp
+++ b/clang-tools-extra/clangd/DraftStore.cpp
@@ -11,6 +11,8 @@
 #include "support/Logger.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/Errc.h"
+#include "llvm/Support/VirtualFileSystem.h"
+#include <memory>
 
 namespace clang {
 namespace clangd {
@@ -22,7 +24,7 @@
   if (It == Drafts.end())
     return None;
 
-  return It->second;
+  return It->second.Draft;
 }
 
 std::vector<Path> DraftStore::getActiveFiles() const {
@@ -75,10 +77,12 @@
                                  llvm::StringRef Contents) {
   std::lock_guard<std::mutex> Lock(Mutex);
 
-  Draft &D = Drafts[File];
-  updateVersion(D, Version);
-  D.Contents = Contents.str();
-  return D.Version;
+  auto Res = Drafts.try_emplace(File);
+  auto &D = Res.first->getValue();
+  updateVersion(D.Draft, Version);
+  time(&D.MTime);
+  D.Draft.Contents = std::make_shared<std::string>(Contents);
+  return D.Draft.Version;
 }
 
 void DraftStore::removeDraft(PathRef File) {
@@ -87,5 +91,38 @@
   Drafts.erase(File);
 }
 
+namespace {
+
+/// A read only MemoryBuffer shares ownership of a ref counted string. The
+/// shared string object must not be modified while an owned by this buffer.
+class SharedStringBuffer : public llvm::MemoryBuffer {
+  const std::shared_ptr<const std::string> BufferContents;
+  const std::string Name;
+
+public:
+  BufferKind getBufferKind() const override {
+    return MemoryBuffer::MemoryBuffer_Malloc;
+  }
+
+  StringRef getBufferIdentifier() const override { return Name; }
+
+  SharedStringBuffer(std::shared_ptr<const std::string> Data, StringRef Name)
+      : BufferContents(std::move(Data)), Name(Name) {
+    assert(BufferContents && "Can't create from empty shared_ptr");
+    MemoryBuffer::init(BufferContents->c_str(),
+                       BufferContents->c_str() + BufferContents->size(), true);
+  }
+};
+} // namespace
+
+llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> DraftStore::asVFS() const {
+  auto MemFS = llvm::makeIntrusiveRefCnt<llvm::vfs::InMemoryFileSystem>();
+  std::lock_guard<std::mutex> Guard(Mutex);
+  for (const auto &Draft : Drafts)
+    MemFS->addFile(Draft.getKey(), Draft.getValue().MTime,
+                   std::make_unique<SharedStringBuffer>(
+                       Draft.getValue().Draft.Contents, Draft.getKey()));
+  return MemFS;
+}
 } // namespace clangd
 } // namespace clang
diff --git a/clang-tools-extra/clangd/unittests/DraftStoreTests.cpp b/clang-tools-extra/clangd/unittests/DraftStoreTests.cpp
--- a/clang-tools-extra/clangd/unittests/DraftStoreTests.cpp
+++ b/clang-tools-extra/clangd/unittests/DraftStoreTests.cpp
@@ -24,20 +24,20 @@
 
   EXPECT_EQ("25", DS.addDraft(File, "25", ""));
   EXPECT_EQ("25", DS.getDraft(File)->Version);
-  EXPECT_EQ("", DS.getDraft(File)->Contents);
+  EXPECT_EQ("", *DS.getDraft(File)->Contents);
 
   EXPECT_EQ("26", DS.addDraft(File, "", "x"));
   EXPECT_EQ("26", DS.getDraft(File)->Version);
-  EXPECT_EQ("x", DS.getDraft(File)->Contents);
+  EXPECT_EQ("x", *DS.getDraft(File)->Contents);
 
   EXPECT_EQ("27", DS.addDraft(File, "", "x")) << "no-op change";
   EXPECT_EQ("27", DS.getDraft(File)->Version);
-  EXPECT_EQ("x", DS.getDraft(File)->Contents);
+  EXPECT_EQ("x", *DS.getDraft(File)->Contents);
 
   // We allow versions to go backwards.
   EXPECT_EQ("7", DS.addDraft(File, "7", "y"));
   EXPECT_EQ("7", DS.getDraft(File)->Version);
-  EXPECT_EQ("y", DS.getDraft(File)->Contents);
+  EXPECT_EQ("y", *DS.getDraft(File)->Contents);
 }
 
 } // namespace