--- boost-posix-2008-03-21.orig/boost/graph/topological_sort.hpp
+++ boost-posix-2008-03-21/boost/graph/topological_sort.hpp
@@ -37,7 +37,7 @@
       : m_iter(_iter) { }
     
     template <typename Edge, typename Graph>
-    void back_edge(const Edge& u, Graph&) { throw not_a_dag(); }
+    void back_edge(const Edge&, Graph&) { throw not_a_dag(); }
     
     template <typename Vertex, typename Graph> 
     void finish_vertex(const Vertex& u, Graph&) { *m_iter++ = u; }