Index: llvm/lib/Support/VirtualFileSystem.cpp
===================================================================
--- llvm/lib/Support/VirtualFileSystem.cpp
+++ llvm/lib/Support/VirtualFileSystem.cpp
@@ -2028,8 +2028,13 @@
   if (!Entries.empty()) {
     const YAMLVFSEntry &Entry = Entries.front();
     bool first_entry_is_directory = Entry.IsDirectory;
-    StringRef Dir =
-        first_entry_is_directory ? Entry.VPath : path::parent_path(Entry.VPath);
+    StringRef Dir;
+    if (first_entry_is_directory) {
+      Dir = Entry.VPath;
+    } else {
+      Dir = path::parent_path(Entry.VPath);
+      assert(!Dir.empty() && "No parent directory");
+    }
     startDirectory(Dir);
 
     StringRef RPath = Entry.RPath;