diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index 358103d..0217a2e 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -149,6 +149,11 @@
     Ident_AbnormalTermination = nullptr;
   }
 
+  // If using a PCH with a through header, start skipping tokens.
+  if (!this->PPOpts->PCHThroughHeader.empty() &&
+      !this->PPOpts->ImplicitPCHInclude.empty())
+    SkippingUntilPCHThroughHeader = true;
+
   if (this->PPOpts->GeneratePreamble)
     PreambleConditionalStack.startRecording();
 }
@@ -551,6 +556,72 @@
 
   // Start parsing the predefines.
   EnterSourceFile(FID, nullptr, SourceLocation());
+
+  if (!PPOpts->PCHThroughHeader.empty()) {
+    // Lookup and save the FileID for the through header. If it isn't found
+    // in the search path, it's a fatal error.
+    const DirectoryLookup *CurDir;
+    const FileEntry *File = LookupFile(
+        SourceLocation(), PPOpts->PCHThroughHeader,
+        /*isAngled=*/false, /*FromDir=*/nullptr, /*FromFile=*/nullptr, CurDir,
+        /*SearchPath=*/nullptr, /*RelativePath=*/nullptr,
+        /*SuggestedModule=*/nullptr, /*IsMapped=*/nullptr);
+    if (!File) {
+      Diag(SourceLocation(), diag::err_pp_through_header_not_found)
+          << PPOpts->PCHThroughHeader;
+      return;
+    }
+    setPCHThroughHeaderFileID(
+        SourceMgr.createFileID(File, SourceLocation(), SrcMgr::C_User));
+  }
+
+  // Skip tokens from the Predefines and if needed the main file.
+  if (usingPCHWithThroughHeader() && SkippingUntilPCHThroughHeader)
+    SkipTokensUntilPCHThroughHeader();
+}
+
+void Preprocessor::setPCHThroughHeaderFileID(FileID FID) {
+  assert(PCHThroughHeaderFileID.isInvalid() &&
+         "PCHThroughHeaderFileID already set!");
+  PCHThroughHeaderFileID = FID;
+}
+
+bool Preprocessor::isPCHThroughHeader(const FileEntry *FE) {
+  assert(PCHThroughHeaderFileID.isValid() &&
+         "Invalid PCH through header FileID");
+  return FE == SourceMgr.getFileEntryForID(PCHThroughHeaderFileID);
+}
+
+bool Preprocessor::creatingPCHWithThroughHeader() {
+  return TUKind == TU_Prefix && !PPOpts->PCHThroughHeader.empty() &&
+         PCHThroughHeaderFileID.isValid();
+}
+
+bool Preprocessor::usingPCHWithThroughHeader() {
+  return TUKind != TU_Prefix && !PPOpts->PCHThroughHeader.empty() &&
+         PCHThroughHeaderFileID.isValid();
+}
+
+/// Skip tokens until after the #include of the through header.
+/// Tokens in the predefines file and the main file may be skipped. If the end
+/// of the predefines file is reached, skipping continues into the main file.
+/// If the end of the main file is reached, it's a fatal error.
+void Preprocessor::SkipTokensUntilPCHThroughHeader() {
+  bool ReachedMainFileEOF = false;
+  Token Tok;
+  while (true) {
+    bool InPredefines = (CurLexer->getFileID() == getPredefinesFileID());
+    CurLexer->Lex(Tok);
+    if (Tok.is(tok::eof) && !InPredefines) {
+      ReachedMainFileEOF = true;
+      break;
+    }
+    if (!SkippingUntilPCHThroughHeader)
+      break;
+  }
+  if (ReachedMainFileEOF)
+    Diag(SourceLocation(), diag::err_pp_through_header_not_seen)
+        << PPOpts->PCHThroughHeader << 1;
 }
 
 void Preprocessor::replayPreambleConditionalStack() {