--- a/src/external/tristripper/detail/graph_array.h
+++ b/src/external/tristripper/detail/graph_array.h
@@ -444,7 +444,10 @@
 template <class N>
 inline void unmark_nodes(graph_array<N> & G)
 {
-  std::for_each(G.begin(), G.end(), std::mem_fun_ref(&graph_array<N>::node::unmark));
+  for (auto& node : G)
+  {
+    node.unmark();
+  }
 }
 
 
