diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index 8143263..d04f785 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -77,6 +77,9 @@
 
 } // anonymous namespace
 
+const std::string &ASTUnit::getOriginalSourceFileName() {
+  return dyn_cast<PCHReader>(Ctx->getExternalSource())->getOriginalSourceFile();
+}
 
 ASTUnit *ASTUnit::LoadFromPCHFile(const std::string &Filename,
                                   FileManager &FileMgr,