diff --git a/llvm/include/llvm/Support/VirtualFileSystem.h b/llvm/include/llvm/Support/VirtualFileSystem.h
--- a/llvm/include/llvm/Support/VirtualFileSystem.h
+++ b/llvm/include/llvm/Support/VirtualFileSystem.h
@@ -506,10 +506,12 @@
 
 struct YAMLVFSEntry {
   template <typename T1, typename T2>
-  YAMLVFSEntry(T1 &&VPath, T2 &&RPath)
-      : VPath(std::forward<T1>(VPath)), RPath(std::forward<T2>(RPath)) {}
+  YAMLVFSEntry(T1 &&VPath, T2 &&RPath, bool IsDirectory = false)
+      : VPath(std::forward<T1>(VPath)), RPath(std::forward<T2>(RPath)),
+        IsDirectory(IsDirectory) {}
   std::string VPath;
   std::string RPath;
+  bool IsDirectory = false;
 };
 
 class VFSFromYamlDirIterImpl;
@@ -771,10 +773,13 @@
   Optional<bool> UseExternalNames;
   std::string OverlayDir;
 
+  void addEntry(StringRef VirtualPath, StringRef RealPath, bool IsDirectory);
+
 public:
   YAMLVFSWriter() = default;
 
   void addFileMapping(StringRef VirtualPath, StringRef RealPath);
+  void addDirectoryMapping(StringRef VirtualPath, StringRef RealPath);
 
   void setCaseSensitivity(bool CaseSensitive) {
     IsCaseSensitive = CaseSensitive;
diff --git a/llvm/lib/Support/VirtualFileSystem.cpp b/llvm/lib/Support/VirtualFileSystem.cpp
--- a/llvm/lib/Support/VirtualFileSystem.cpp
+++ b/llvm/lib/Support/VirtualFileSystem.cpp
@@ -1912,11 +1912,21 @@
   return UniqueID(std::numeric_limits<uint64_t>::max(), ID);
 }
 
-void YAMLVFSWriter::addFileMapping(StringRef VirtualPath, StringRef RealPath) {
+void YAMLVFSWriter::addEntry(StringRef VirtualPath, StringRef RealPath,
+                             bool IsDirectory) {
   assert(sys::path::is_absolute(VirtualPath) && "virtual path not absolute");
   assert(sys::path::is_absolute(RealPath) && "real path not absolute");
   assert(!pathHasTraversal(VirtualPath) && "path traversal is not supported");
-  Mappings.emplace_back(VirtualPath, RealPath);
+  Mappings.emplace_back(VirtualPath, RealPath, IsDirectory);
+}
+
+void YAMLVFSWriter::addFileMapping(StringRef VirtualPath, StringRef RealPath) {
+  addEntry(VirtualPath, RealPath, /*IsDirectory=*/false);
+}
+
+void YAMLVFSWriter::addDirectoryMapping(StringRef VirtualPath,
+                                        StringRef RealPath) {
+  addEntry(VirtualPath, RealPath, /*IsDirectory=*/true);
 }
 
 namespace {
@@ -2017,7 +2027,10 @@
 
   if (!Entries.empty()) {
     const YAMLVFSEntry &Entry = Entries.front();
-    startDirectory(path::parent_path(Entry.VPath));
+    bool first_entry_is_directory = Entry.IsDirectory;
+    StringRef Dir =
+        first_entry_is_directory ? Entry.VPath : path::parent_path(Entry.VPath);
+    startDirectory(Dir);
 
     StringRef RPath = Entry.RPath;
     if (UseOverlayRelative) {
@@ -2027,13 +2040,18 @@
       RPath = RPath.slice(OverlayDirLen, RPath.size());
     }
 
-    writeEntry(path::filename(Entry.VPath), RPath);
+    if (!first_entry_is_directory)
+      writeEntry(path::filename(Entry.VPath), RPath);
 
     for (const auto &Entry : Entries.slice(1)) {
-      StringRef Dir = path::parent_path(Entry.VPath);
-      if (Dir == DirStack.back())
-        OS << ",\n";
-      else {
+      StringRef Dir =
+          Entry.IsDirectory ? Entry.VPath : path::parent_path(Entry.VPath);
+      if (Dir == DirStack.back()) {
+        if (!first_entry_is_directory) {
+          OS << ",\n";
+          first_entry_is_directory = false;
+        }
+      } else {
         while (!DirStack.empty() && !containedIn(DirStack.back(), Dir)) {
           OS << "\n";
           endDirectory();
diff --git a/llvm/unittests/Support/VirtualFileSystemTest.cpp b/llvm/unittests/Support/VirtualFileSystemTest.cpp
--- a/llvm/unittests/Support/VirtualFileSystemTest.cpp
+++ b/llvm/unittests/Support/VirtualFileSystemTest.cpp
@@ -2200,20 +2200,14 @@
   ScopedDir _g(TestDirectory + "/g");
   ScopedFile _h(TestDirectory + "/h", "");
 
-  // This test exposes a bug/shortcoming in the YAMLVFSWriter. Below we call
-  // addFileMapping for _a and _e, which causes _ab and _ef not to exists in
-  // the deserialized file system, because _a and _e got emitted as regular
-  // files. The counter example is _c, if we only call addFileMapping for _cd,
-  // things work as expected.
-
   vfs::YAMLVFSWriter VFSWriter;
-  VFSWriter.addFileMapping(_a.Path, "//root/a");
+  VFSWriter.addDirectoryMapping(_a.Path, "//root/a");
   VFSWriter.addFileMapping(_ab.Path, "//root/a/b");
   VFSWriter.addFileMapping(_cd.Path, "//root/c/d");
-  VFSWriter.addFileMapping(_e.Path, "//root/e");
-  VFSWriter.addFileMapping(_ef.Path, "//root/e/f");
+  VFSWriter.addDirectoryMapping(_e.Path, "//root/e");
+  VFSWriter.addDirectoryMapping(_ef.Path, "//root/e/f");
   VFSWriter.addFileMapping(_g.Path, "//root/g");
-  VFSWriter.addFileMapping(_h.Path, "//root/h");
+  VFSWriter.addDirectoryMapping(_h.Path, "//root/h");
 
   std::string Buffer;
   raw_string_ostream OS(Buffer);
@@ -2236,11 +2230,11 @@
   ASSERT_TRUE(FS.get() != nullptr);
 
   EXPECT_TRUE(FS->exists(_a.Path));
-  EXPECT_FALSE(FS->exists(_ab.Path)); // FIXME: See explanation above.
+  EXPECT_TRUE(FS->exists(_ab.Path));
   EXPECT_TRUE(FS->exists(_c.Path));
   EXPECT_TRUE(FS->exists(_cd.Path));
   EXPECT_TRUE(FS->exists(_e.Path));
-  EXPECT_FALSE(FS->exists(_ef.Path)); // FIXME: See explanation above.
+  EXPECT_TRUE(FS->exists(_ef.Path));
   EXPECT_TRUE(FS->exists(_g.Path));
   EXPECT_TRUE(FS->exists(_h.Path));
 }