diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index 5e3fa13..3dcc62e 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -1181,6 +1181,39 @@
   }
 }
 
+/// \brief If a header file is not found at the path that we expect it to be
+/// and the PCH file was moved from its original location, try to resolve the
+/// file by assuming that header+PCH were moved together and the header is in
+/// the same place relative to the PCH.
+static std::string
+resolveFileRelativeToOriginalDir(const std::string &Filename,
+                                 const std::string &OriginalDir,
+                                 const std::string &CurrDir) {
+  assert(OriginalDir != CurrDir &&
+         "No point trying to resolve the file if the PCH dir didn't change");
+  using namespace llvm::sys;
+  llvm::SmallString<128> filePath(Filename);
+  fs::make_absolute(filePath);
+  assert(path::is_absolute(OriginalDir));
+  llvm::SmallString<128> currPCHPath(CurrDir);
+
+  path::const_iterator fileDirI = path::begin(path::parent_path(filePath)),
+                       fileDirE = path::end(path::parent_path(filePath));
+  path::const_iterator origDirI = path::begin(OriginalDir),
+                       origDirE = path::end(OriginalDir);
+  // Skip the common path components from filePath and OriginalDir.
+  while (fileDirI != fileDirE && origDirI != origDirE &&
+         *fileDirI == *origDirI) {
+    ++fileDirI;
+    ++origDirI;
+  }
+  for (; origDirI != origDirE; ++origDirI)
+    path::append(currPCHPath, "..");
+  path::append(currPCHPath, fileDirI, fileDirE);
+  path::append(currPCHPath, path::filename(Filename));
+  return currPCHPath.str();
+}
+
 /// \brief Get a cursor that's correctly positioned for reading the source
 /// location entry with the given ID.
 ASTReader::PerFileData *ASTReader::SLocCursorForID(unsigned ID) {
@@ -1235,6 +1268,14 @@
     std::string Filename(BlobStart, BlobStart + BlobLen);
     MaybeAddSystemRootToFilename(Filename);
     const FileEntry *File = FileMgr.getFile(Filename);
+    if (File == 0 && !OriginalDir.empty() && !CurrentDir.empty() &&
+        OriginalDir != CurrentDir) {
+      std::string resolved = resolveFileRelativeToOriginalDir(Filename,
+                                                              OriginalDir,
+                                                              CurrentDir);
+      if (!resolved.empty())
+        File = FileMgr.getFile(resolved);
+    }
     if (File == 0)
       File = FileMgr.getVirtualFile(Filename, (off_t)Record[4],
                                     (time_t)Record[5]);
@@ -2179,6 +2220,12 @@
       MaybeAddSystemRootToFilename(OriginalFileName);
       break;
 
+    case ORIGINAL_PCH_DIR:
+      // The primary AST will be the last to get here, so it will be the one
+      // that's used.
+      OriginalDir.assign(BlobStart, BlobLen);
+      break;
+
     case VERSION_CONTROL_BRANCH_REVISION: {
       const std::string &CurBranch = getClangFullRepositoryVersion();
       llvm::StringRef ASTBranch(BlobStart, BlobLen);
@@ -2393,6 +2440,11 @@
   // Set the AST file name.
   F.FileName = FileName;
 
+  if (FileName != "-") {
+    CurrentDir = llvm::sys::path::parent_path(FileName);
+    if (CurrentDir.empty()) CurrentDir = ".";
+  }
+
   // Open the AST file.
   //
   // FIXME: This shouldn't be here, we should just take a raw_ostream.
diff --git a/lib/Serialization/ASTWriter.cpp b/lib/Serialization/ASTWriter.cpp
index f1af835..cb29973 100644
--- a/lib/Serialization/ASTWriter.cpp
+++ b/lib/Serialization/ASTWriter.cpp
@@ -899,7 +899,8 @@
 }
 
 /// \brief Write the AST metadata (e.g., i686-apple-darwin9).
-void ASTWriter::WriteMetadata(ASTContext &Context, const char *isysroot) {
+void ASTWriter::WriteMetadata(ASTContext &Context, const char *isysroot,
+                              const std::string &OutputFile) {
   using namespace llvm;
 
   // Metadata
@@ -947,6 +948,23 @@
     Stream.EmitRecordWithBlob(FileAbbrevCode, Record, MainFileNameStr);
   }
 
+  // Original PCH directory
+  if (!OutputFile.empty() && OutputFile != "-") {
+    BitCodeAbbrev *Abbrev = new BitCodeAbbrev();
+    Abbrev->Add(BitCodeAbbrevOp(ORIGINAL_PCH_DIR));
+    Abbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Blob)); // File name
+    unsigned AbbrevCode = Stream.EmitAbbrev(Abbrev);
+
+    llvm::SmallString<128> OutputPath(OutputFile);
+
+    llvm::sys::fs::make_absolute(OutputPath);
+    StringRef origDir = llvm::sys::path::parent_path(OutputPath);
+
+    RecordData Record;
+    Record.push_back(ORIGINAL_PCH_DIR);
+    Stream.EmitRecordWithBlob(AbbrevCode, Record, origDir);
+  }
+
   // Repository branch/version information.
   BitCodeAbbrev *RepoAbbrev = new BitCodeAbbrev();
   RepoAbbrev->Add(BitCodeAbbrevOp(VERSION_CONTROL_BRANCH_REVISION));
@@ -2568,6 +2586,7 @@
 }
 
 void ASTWriter::WriteAST(Sema &SemaRef, MemorizeStatCalls *StatCalls,
+                         const std::string &OutputFile,
                          const char *isysroot) {
   // Emit the file header.
   Stream.Emit((unsigned)'C', 8);
@@ -2580,11 +2599,12 @@
   if (Chain)
     WriteASTChain(SemaRef, StatCalls, isysroot);
   else
-    WriteASTCore(SemaRef, StatCalls, isysroot);
+    WriteASTCore(SemaRef, StatCalls, isysroot, OutputFile);
 }
 
 void ASTWriter::WriteASTCore(Sema &SemaRef, MemorizeStatCalls *StatCalls,
-                             const char *isysroot) {
+                             const char *isysroot,
+                             const std::string &OutputFile) {
   using namespace llvm;
 
   ASTContext &Context = SemaRef.Context;
@@ -2692,7 +2712,7 @@
   // Write the remaining AST contents.
   RecordData Record;
   Stream.EnterSubblock(AST_BLOCK_ID, 5);
-  WriteMetadata(Context, isysroot);
+  WriteMetadata(Context, isysroot, OutputFile);
   WriteLanguageOptions(Context.getLangOptions());
   if (StatCalls && !isysroot)
     WriteStatCache(*StatCalls);
@@ -2827,7 +2847,7 @@
 
   RecordData Record;
   Stream.EnterSubblock(AST_BLOCK_ID, 5);
-  WriteMetadata(Context, isysroot);
+  WriteMetadata(Context, isysroot, "");
   if (StatCalls && !isysroot)
     WriteStatCache(*StatCalls);
   // FIXME: Source manager block should only write new stuff, which could be
diff --git a/lib/Serialization/GeneratePCH.cpp b/lib/Serialization/GeneratePCH.cpp
index 3b4f869..b8833ce 100644
--- a/lib/Serialization/GeneratePCH.cpp
+++ b/lib/Serialization/GeneratePCH.cpp
@@ -27,10 +27,11 @@
 using namespace clang;
 
 PCHGenerator::PCHGenerator(const Preprocessor &PP,
+                           const std::string &OutputFile,
                            bool Chaining,
                            const char *isysroot,
                            llvm::raw_ostream *OS)
-  : PP(PP), isysroot(isysroot), Out(OS), SemaPtr(0),
+  : PP(PP), OutputFile(OutputFile), isysroot(isysroot), Out(OS), SemaPtr(0),
     StatCalls(0), Stream(Buffer), Writer(Stream), Chaining(Chaining) {
   // Install a stat() listener to keep track of all of the stat()
   // calls.
@@ -50,7 +51,7 @@
   
   // Emit the PCH file
   assert(SemaPtr && "No Sema?");
-  Writer.WriteAST(*SemaPtr, StatCalls, isysroot);
+  Writer.WriteAST(*SemaPtr, StatCalls, OutputFile, isysroot);
 
   // Write the generated bitstream to "Out".
   Out->write((char *)&Buffer.front(), Buffer.size());