diff --git a/lib/Basic/SourceManager.cpp b/lib/Basic/SourceManager.cpp
index 8dfc5d1..23a01c9 100644
--- a/lib/Basic/SourceManager.cpp
+++ b/lib/Basic/SourceManager.cpp
@@ -373,7 +373,10 @@
   
   // Set LastFileIDLookup to the newly created file.  The next getFileID call is
   // almost guaranteed to be from that file.
-  return LastFileIDLookup = FileID::get(SLocEntryTable.size()-1);
+  FileID FID = FileID::get(SLocEntryTable.size()-1);
+  if (File->FirstFID.isInvalid())
+    File->FirstFID = FID;
+  return LastFileIDLookup = FID;
 }
 
 /// createInstantiationLoc - Return a new SourceLocation that encodes the fact