Index: lib/Serialization/ASTReader.cpp
===================================================================
--- lib/Serialization/ASTReader.cpp
+++ lib/Serialization/ASTReader.cpp
@@ -3655,6 +3655,8 @@
   if (EC)
     return;
   OS << "Timestamp file\n";
+  OS.close();
+  OS.clear_error(); // Avoid triggering a fatal error.
 }
 
 /// \brief Given a cursor at the start of an AST file, scan ahead and drop the