Create alternative list only as needed.

1 files changed, 1 insertions, 1 deletions

diff --git a/session.h b/session.h
index 6ae44fe2..f49edd46 100644
--- a/session.h
+++ b/session.h
@@ -167,7 +167,7 @@ struct systemtap_session
   unsigned num_errors () { return seen_errors.size(); }
   // void print_error (const parse_error& e);
   void print_error (const semantic_error& e);
-  void print_warning (const std::string& w, std::string o);
+  void print_warning (const std::string& w, const std::string& o);
 
   // reNB: new POD members likely need to be explicitly cleared in the ctor.
 };