diff --git a/src/libraries/turtle/action.hpp b/src/libraries/turtle/action.hpp
index 2d51c33..09656a4 100644
--- a/src/libraries/turtle/action.hpp
+++ b/src/libraries/turtle/action.hpp
@@ -213,7 +213,7 @@ namespace detail
             f_ = lambda_type::make_val( boost::ref( r_ ) );
         }
 
-        mutable std::auto_ptr< Result > r_;
+        std::auto_ptr< Result > r_;
         functor_type f_;
     };