diff -r 07cd9a2d20e0 -r ce1533650f7d lemon/network_simplex.h
--- a/lemon/network_simplex.h	Mon Jul 07 11:23:41 2014 +0200
+++ b/lemon/network_simplex.h	Mon Jul 07 15:40:12 2014 +0200
@@ -936,7 +936,7 @@
       for (NodeIt n(_graph); n != INVALID; ++n, ++i) {
         _node_id[n] = i;
       }
-      if (_arc_mixing) {
+      if (_arc_mixing && _node_num > 1) {
         // Store the arcs in a mixed order
         const int skip = std::max(_arc_num / _node_num, 3);
         int i = 0, j = 0;