diff --git a/ChangeLog b/ChangeLog
index 8d9c170b2..bfeaa50db 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2008-01-10  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
+
+	* src/tgbaalgos/reductgba_sim.cc (reduc_tgba_sim): Add two
+	assert().  This patch has been lying in my tree since 2007-04-30.
+
 2008-01-08  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
 
 	This is something Soheib and I worked on back in July, but a
diff --git a/src/tgbaalgos/reductgba_sim.cc b/src/tgbaalgos/reductgba_sim.cc
index 7590c027f..3aae15504 100644
--- a/src/tgbaalgos/reductgba_sim.cc
+++ b/src/tgbaalgos/reductgba_sim.cc
@@ -1,4 +1,4 @@
-// Copyright (C) 2004, 2005  Laboratoire d'Informatique de Paris 6 (LIP6),
+// Copyright (C) 2004, 2005, 2007  Laboratoire d'Informatique de Paris 6 (LIP6),
 // département Systèmes Répartis Coopératifs (SRC), Université Pierre
 // et Marie Curie.
 //
@@ -673,6 +673,8 @@ namespace spot
 	direct_simulation_relation* rel
 	  = get_direct_relation_simulation(automatareduc, std::cout);
 
+	assert(rel);
+
 	automatareduc->display_rel_sim(rel, std::cout);
 	automatareduc->quotient_state(rel);
 	automatareduc->delete_transitions(rel);
@@ -685,6 +687,8 @@ namespace spot
 	  delayed_simulation_relation* rel
 	    = get_delayed_relation_simulation(automatareduc, std::cout);
 
+	  assert(rel);
+
 	  automatareduc->display_rel_sim(rel, std::cout);
 	  automatareduc->quotient_state(rel);
 	  automatareduc->delete_transitions(rel);