diff --git a/lemon/bellman_ford.h b/lemon/bellman_ford.h
--- a/lemon/bellman_ford.h
+++ b/lemon/bellman_ford.h
@@ -23,6 +23,7 @@
 /// \file
 /// \brief Bellman-Ford algorithm.
 
+#include <lemon/list_graph.h>
 #include <lemon/bits/path_dump.h>
 #include <lemon/core.h>
 #include <lemon/error.h>
@@ -775,7 +776,7 @@
     /// This function gives back a directed cycle with negative total
     /// length if the algorithm has already found one.
     /// Otherwise it gives back an empty path.
-    lemon::Path<Digraph> negativeCycle() {
+    lemon::Path<Digraph> negativeCycle() const {
       typename Digraph::template NodeMap<int> state(*_gr, -1);
       lemon::Path<Digraph> cycle;
       for (int i = 0; i < int(_process.size()); ++i) {
diff --git a/test/bellman_ford_test.cc b/test/bellman_ford_test.cc
--- a/test/bellman_ford_test.cc
+++ b/test/bellman_ford_test.cc
@@ -96,6 +96,7 @@
     d  = const_bf_test.distMap();
     p  = const_bf_test.predMap();
     pp = const_bf_test.path(t);
+    pp = const_bf_test.negativeCycle();
     
     for (BF::ActiveIt it(const_bf_test); it != INVALID; ++it) {}
   }
@@ -132,6 +133,7 @@
     s  = bf_test.predNode(t);
     b  = bf_test.reached(t);
     pp = bf_test.path(t);
+    pp = bf_test.negativeCycle();
   }
 }