Index: include/clang/Basic/IdentifierTable.h
===================================================================
--- include/clang/Basic/IdentifierTable.h
+++ include/clang/Basic/IdentifierTable.h
@@ -477,9 +477,11 @@
 
 public:
   /// \brief Create the identifier table, populating it with info about the
-  /// language keywords for the language specified by \p LangOpts.
+  /// language keywords for the language specified by \p LangOpts if
+  /// \p DeferKeywordAddition is not set.
   IdentifierTable(const LangOptions &LangOpts,
-                  IdentifierInfoLookup* externalLookup = nullptr);
+                  IdentifierInfoLookup *externalLookup = nullptr,
+                  bool DeferKeywordAddition = false);
 
   /// \brief Set the external identifier lookup mechanism.
   void setExternalIdentifierLookup(IdentifierInfoLookup *IILookup) {
Index: include/clang/Lex/Preprocessor.h
===================================================================
--- include/clang/Lex/Preprocessor.h
+++ include/clang/Lex/Preprocessor.h
@@ -691,7 +691,8 @@
                HeaderSearch &Headers, ModuleLoader &TheModuleLoader,
                IdentifierInfoLookup *IILookup = nullptr,
                bool OwnsHeaderSearch = false,
-               TranslationUnitKind TUKind = TU_Complete);
+               TranslationUnitKind TUKind = TU_Complete,
+               bool DeferKeywordAddition = false);
 
   ~Preprocessor();
 
Index: lib/Basic/IdentifierTable.cpp
===================================================================
--- lib/Basic/IdentifierTable.cpp
+++ lib/Basic/IdentifierTable.cpp
@@ -73,17 +73,15 @@
 }
 
 IdentifierTable::IdentifierTable(const LangOptions &LangOpts,
-                                 IdentifierInfoLookup* externalLookup)
-  : HashTable(8192), // Start with space for 8K identifiers.
-    ExternalLookup(externalLookup) {
+                                 IdentifierInfoLookup *externalLookup,
+                                 bool DeferKeywordAddition)
+    : HashTable(8192), // Start with space for 8K identifiers.
+      ExternalLookup(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);
+  if (!DeferKeywordAddition)
+    AddKeywords(LangOpts);
 }
 
 //===----------------------------------------------------------------------===//
@@ -227,6 +225,9 @@
 
   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/Frontend/ASTUnit.cpp
===================================================================
--- lib/Frontend/ASTUnit.cpp
+++ lib/Frontend/ASTUnit.cpp
@@ -536,6 +536,10 @@
     // Initialize the preprocessor.
     PP.Initialize(*Target);
 
+    // Populate the identifier table with info about keywords for the current
+    // language.
+    PP.getIdentifierTable().AddKeywords(LangOpt);
+
     if (!Context)
       return;
 
@@ -718,11 +722,13 @@
   HeaderSearch &HeaderInfo = *AST->HeaderInfo;
   unsigned Counter;
 
+  // As the language options have not been loaded yet, adding keywords to the
+  // identifier table is deferred and will be initiated by ASTInfoCollector.
   AST->PP = std::make_shared<Preprocessor>(
       AST->PPOpts, AST->getDiagnostics(), *AST->LangOpts,
       AST->getSourceManager(), *AST->PCMCache, HeaderInfo, AST->ModuleLoader,
-      /*IILookup=*/nullptr,
-      /*OwnsHeaderSearch=*/false);
+      /*IILookup=*/nullptr, /*OwnsHeaderSearch=*/false, TU_Complete,
+      /*DeferKeywordAddition=*/true);
   Preprocessor &PP = *AST->PP;
 
   if (ToLoad >= LoadASTOnly)
Index: lib/Lex/Preprocessor.cpp
===================================================================
--- lib/Lex/Preprocessor.cpp
+++ lib/Lex/Preprocessor.cpp
@@ -73,12 +73,14 @@
                            SourceManager &SM, MemoryBufferCache &PCMCache,
                            HeaderSearch &Headers, ModuleLoader &TheModuleLoader,
                            IdentifierInfoLookup *IILookup, bool OwnsHeaders,
-                           TranslationUnitKind TUKind)
+                           TranslationUnitKind TUKind,
+                           bool DeferKeywordAddition)
     : PPOpts(std::move(PPOpts)), Diags(&diags), LangOpts(opts), Target(nullptr),
       AuxTarget(nullptr), FileMgr(Headers.getFileMgr()), SourceMgr(SM),
       PCMCache(PCMCache), ScratchBuf(new ScratchBuffer(SourceMgr)),
       HeaderInfo(Headers), TheModuleLoader(TheModuleLoader),
-      ExternalSource(nullptr), Identifiers(opts, IILookup),
+      ExternalSource(nullptr),
+      Identifiers(opts, IILookup, DeferKeywordAddition),
       PragmaHandlers(new PragmaNamespace(StringRef())),
       IncrementalProcessing(false), TUKind(TUKind), CodeComplete(nullptr),
       CodeCompletionFile(nullptr), CodeCompletionOffset(0),
Index: unittests/libclang/LibclangTest.cpp
===================================================================
--- unittests/libclang/LibclangTest.cpp
+++ unittests/libclang/LibclangTest.cpp
@@ -572,3 +572,67 @@
   EXPECT_EQ(0U, clang_getNumDiagnostics(ClangTU));
   DisplayDiagnostics();
 }
+
+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();
+}