diff --git a/ChangeLog b/ChangeLog
index dd53ae7da..2017a07bc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2004-12-14  Denis Poitrenaud  <Denis.Poitrenaud@lip6.fr>
+
+	* src/tgbaalgos/ndfs_result.hh: Define the trace output stream.
+
 2004-12-13  Denis Poitrenaud  <Denis.Poitrenaud@lip6.fr>
 
 	* src/tgbaalgos/ndfs_result.hh: New file factorizing the computation of
diff --git a/src/tgbaalgos/ndfs_result.hh b/src/tgbaalgos/ndfs_result.hh
index d286016bb..cbedaba43 100644
--- a/src/tgbaalgos/ndfs_result.hh
+++ b/src/tgbaalgos/ndfs_result.hh
@@ -22,6 +22,15 @@
 #ifndef SPOT_TGBAALGOS_NDFS_RESULT_HH
 # define SPOT_TGBAALGOS_NDFS_RESULT_HH
 
+//#define TRACE
+
+#include <iostream>
+#ifdef TRACE
+#define trace std::cerr
+#else
+#define trace while (0) std::cerr
+#endif
+
 #include <cassert>
 #include <list>
 #include "tgba/tgba.hh"