diff --git a/Basic/SourceManager.cpp b/Basic/SourceManager.cpp
index d7039b3..fe21342 100644
--- a/Basic/SourceManager.cpp
+++ b/Basic/SourceManager.cpp
@@ -508,6 +508,7 @@
 void SourceManager::Emit(llvm::Serializer& S) const {
   S.EnterBlock();
   S.EmitPtr(this);
+  S.EmitInt(MainFileID);
   
   // Emit: FileInfos.  Just emit the file name.
   S.EnterBlock();    
@@ -541,6 +542,9 @@
   SourceManager *M = new SourceManager();
   D.RegisterPtr(M);
   
+  // Read: the FileID of the main source file of the translation unit.
+  M->MainFileID = D.ReadInt();
+  
   std::vector<char> Buf;
     
   { // Read: FileInfos.