Index: include/clang/Basic/IdentifierTable.h
===================================================================
--- include/clang/Basic/IdentifierTable.h
+++ include/clang/Basic/IdentifierTable.h
@@ -467,10 +467,13 @@
   IdentifierInfoLookup* ExternalLookup;
 
 public:
+  /// \brief Create the identifier table.
+  explicit IdentifierTable(IdentifierInfoLookup *ExternalLookup = nullptr);
+
   /// \brief Create the identifier table, populating it with info about the
   /// language keywords for the language specified by \p LangOpts.
-  IdentifierTable(const LangOptions &LangOpts,
-                  IdentifierInfoLookup* externalLookup = nullptr);
+  explicit IdentifierTable(const LangOptions &LangOpts,
+                           IdentifierInfoLookup *ExternalLookup = nullptr);
 
   /// \brief Set the external identifier lookup mechanism.
   void setExternalIdentifierLookup(IdentifierInfoLookup *IILookup) {
@@ -558,6 +561,8 @@
   /// hashing is doing.
   void PrintStats() const;
 
+  /// \brief Populate the identifier table with info about the language keywords
+  /// for the language specified by \p LangOpts.
   void AddKeywords(const LangOptions &LangOpts);
 };
 
Index: lib/Basic/IdentifierTable.cpp
===================================================================
--- lib/Basic/IdentifierTable.cpp
+++ lib/Basic/IdentifierTable.cpp
@@ -79,16 +79,16 @@
   return new EmptyLookupIterator();
 }
 
+IdentifierTable::IdentifierTable(IdentifierInfoLookup *ExternalLookup)
+    : HashTable(8192), // Start with space for 8K identifiers.
+      ExternalLookup(ExternalLookup) {}
+
 IdentifierTable::IdentifierTable(const LangOptions &LangOpts,
-                                 IdentifierInfoLookup* externalLookup)
-  : HashTable(8192), // Start with space for 8K identifiers.
-    ExternalLookup(externalLookup) {
+                                 IdentifierInfoLookup *ExternalLookup)
+    : IdentifierTable(ExternalLookup) {
   // Populate the identifier table with info about keywords for the current
   // language.
   AddKeywords(LangOpts);
-
-  // Add the '_experimental_modules_import' contextual keyword.
-  get("import").setModulesImport(true);
 }
 
 //===----------------------------------------------------------------------===//
@@ -237,6 +237,9 @@
 
   if (LangOpts.DeclSpecKeyword)
     AddKeyword("__declspec", tok::kw___declspec, KEYALL, LangOpts, *this);
+
+  // Add the '_experimental_modules_import' contextual keyword.
+  get("import").setModulesImport(true);
 }
 
 /// \brief Checks if the specified token kind represents a keyword in the
Index: lib/Lex/Preprocessor.cpp
===================================================================
--- lib/Lex/Preprocessor.cpp
+++ lib/Lex/Preprocessor.cpp
@@ -85,12 +85,14 @@
                            IdentifierInfoLookup *IILookup, bool OwnsHeaders,
                            TranslationUnitKind TUKind)
     : PPOpts(std::move(PPOpts)), Diags(&diags), LangOpts(opts),
-      FileMgr(Headers.getFileMgr()), SourceMgr(SM),
-      PCMCache(PCMCache), ScratchBuf(new ScratchBuffer(SourceMgr)),
-      HeaderInfo(Headers), TheModuleLoader(TheModuleLoader),
-      ExternalSource(nullptr), Identifiers(opts, IILookup),
-      PragmaHandlers(new PragmaNamespace(StringRef())), TUKind(TUKind),
-      SkipMainFilePreamble(0, true),
+      FileMgr(Headers.getFileMgr()), SourceMgr(SM), PCMCache(PCMCache),
+      ScratchBuf(new ScratchBuffer(SourceMgr)), HeaderInfo(Headers),
+      TheModuleLoader(TheModuleLoader), ExternalSource(nullptr),
+      // As the language options may have not been loaded yet (when
+      // deserializing an ASTUnit), adding keywords to the identifier table is
+      // deferred to Preprocessor::Initialize().
+      Identifiers(IILookup), PragmaHandlers(new PragmaNamespace(StringRef())),
+      TUKind(TUKind), SkipMainFilePreamble(0, true),
       CurSubmoduleState(&NullSubmoduleState) {
   OwnsHeaderSearch = OwnsHeaders;
   
@@ -190,6 +192,9 @@
   // Initialize information about built-ins.
   BuiltinInfo.InitializeTarget(Target, AuxTarget);
   HeaderInfo.setTarget(Target);
+
+  // Populate the identifier table with info about keywords for the current language.
+  Identifiers.AddKeywords(LangOpts);
 }
 
 void Preprocessor::InitializeForModelFile() {
Index: unittests/libclang/LibclangTest.cpp
===================================================================
--- unittests/libclang/LibclangTest.cpp
+++ unittests/libclang/LibclangTest.cpp
@@ -698,3 +698,67 @@
     clang_disposeSourceRangeList(Ranges);
   }
 }
+
+class LibclangSerializationTest : public LibclangParseTest {
+public:
+  bool SaveAndLoadTU(const std::string &Filename) {
+    unsigned options = clang_defaultSaveOptions(ClangTU);
+    if (clang_saveTranslationUnit(ClangTU, Filename.c_str(), options) !=
+        CXSaveError_None) {
+      DEBUG(llvm::dbgs() << "Saving failed\n");
+      return false;
+    }
+
+    clang_disposeTranslationUnit(ClangTU);
+
+    ClangTU = clang_createTranslationUnit(Index, Filename.c_str());
+
+    if (!ClangTU) {
+      DEBUG(llvm::dbgs() << "Loading failed\n");
+      return false;
+    }
+
+    return true;
+  }
+};
+
+TEST_F(LibclangSerializationTest, TokenKindsAreCorrectAfterLoading) {
+  // Ensure that "class" is recognized as a keyword token after serializing
+  // and reloading the AST, as it is not a keyword for the default LangOptions.
+  std::string HeaderName = "test.h";
+  WriteFile(HeaderName, "enum class Something {};");
+
+  const char *Argv[] = {"-xc++-header", "-std=c++11"};
+
+  ClangTU = clang_parseTranslationUnit(Index, HeaderName.c_str(), Argv,
+                                       sizeof(Argv) / sizeof(Argv[0]), nullptr,
+                                       0, TUFlags);
+
+  auto CheckTokenKinds = [=]() {
+    CXSourceRange Range =
+        clang_getCursorExtent(clang_getTranslationUnitCursor(ClangTU));
+
+    CXToken *Tokens;
+    unsigned int NumTokens;
+    clang_tokenize(ClangTU, Range, &Tokens, &NumTokens);
+
+    ASSERT_EQ(6u, NumTokens);
+    EXPECT_EQ(CXToken_Keyword, clang_getTokenKind(Tokens[0]));
+    EXPECT_EQ(CXToken_Keyword, clang_getTokenKind(Tokens[1]));
+    EXPECT_EQ(CXToken_Identifier, clang_getTokenKind(Tokens[2]));
+    EXPECT_EQ(CXToken_Punctuation, clang_getTokenKind(Tokens[3]));
+    EXPECT_EQ(CXToken_Punctuation, clang_getTokenKind(Tokens[4]));
+    EXPECT_EQ(CXToken_Punctuation, clang_getTokenKind(Tokens[5]));
+
+    clang_disposeTokens(ClangTU, Tokens, NumTokens);
+  };
+
+  CheckTokenKinds();
+
+  std::string ASTName = "test.ast";
+  WriteFile(ASTName, "");
+
+  ASSERT_TRUE(SaveAndLoadTU(ASTName));
+
+  CheckTokenKinds();
+}