diff --git a/clang/unittests/Tooling/TransformerTest.cpp b/clang/unittests/Tooling/TransformerTest.cpp
@@ -17,6 +17,7 @@
 #include "llvm/Support/Error.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
+#include <optional>
 
 using namespace clang;
 using namespace tooling;

diff --git a/clang/utils/TableGen/ASTTableGen.cpp b/clang/utils/TableGen/ASTTableGen.cpp
@@ -15,6 +15,7 @@
 #include "ASTTableGen.h"
 #include "llvm/TableGen/Record.h"
 #include "llvm/TableGen/Error.h"
+#include <optional>
 
 using namespace llvm;
 using namespace clang;

diff --git a/clang/utils/TableGen/ASTTableGen.h b/clang/utils/TableGen/ASTTableGen.h
@@ -11,6 +11,7 @@
 
 #include "llvm/TableGen/Record.h"
 #include "llvm/ADT/STLExtras.h"
+#include <optional>
 
 // These are spellings in the tblgen files.
 

diff --git a/clang/utils/TableGen/ClangASTPropertiesEmitter.cpp b/clang/utils/TableGen/ClangASTPropertiesEmitter.cpp
@@ -20,6 +20,7 @@
 #include "llvm/TableGen/TableGenBackend.h"
 #include <cctype>
 #include <map>
+#include <optional>
 #include <set>
 #include <string>
 using namespace llvm;

diff --git a/clang/utils/TableGen/ClangAttrEmitter.cpp b/clang/utils/TableGen/ClangAttrEmitter.cpp
@@ -37,6 +37,7 @@
 #include <cstdint>
 #include <map>
 #include <memory>
+#include <optional>
 #include <set>
 #include <sstream>
 #include <string>