diff --git a/ChangeLog b/ChangeLog
index 99526b42a..4864f8c64 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2009-11-18  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
+
+	Make it easy to filter states while iterating over an automaton.
+
+	* src/tgbaalgos/reachiter.hh (tgba_reachable_iterator::want_state):
+	New method.
+	* src/tgbaalgos/reachiter.cc (tgba_reachable_iterator::want_state):
+	Implement it.
+	(tgba_reachable_iterator::run): Call want_state before processing
+	a state.
+
 2009-11-17  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
 
 	* src/tgbaalgos/cutscc.cc (cut_scc): Pass `s' by reference instead
diff --git a/src/tgbaalgos/reachiter.cc b/src/tgbaalgos/reachiter.cc
index d45776d5a..1be3de987 100644
--- a/src/tgbaalgos/reachiter.cc
+++ b/src/tgbaalgos/reachiter.cc
@@ -1,4 +1,4 @@
-// Copyright (C) 2003, 2004  Laboratoire d'Informatique de Paris 6 (LIP6),
+// Copyright (C) 2003, 2004, 2009  Laboratoire d'Informatique de Paris 6 (LIP6),
 // département Systèmes Répartis Coopératifs (SRC), Université Pierre
 // et Marie Curie.
 //
@@ -50,7 +50,8 @@ namespace spot
     int n = 0;
     start();
     state* i = automata_->get_init_state();
-    add_state(i);
+    if (want_state(i))
+      add_state(i);
     seen[i] = ++n;
     const state* t;
     while ((t = next_state()))
@@ -63,15 +64,20 @@ namespace spot
 	  {
 	    const state* current = si->current_state();
 	    seen_map::const_iterator s = seen.find(current);
+	    bool ws = want_state(current);
 	    if (s == seen.end())
 	      {
 		seen[current] = ++n;
-		add_state(current);
-		process_link(t, tn, current, n, si);
+		if (ws)
+		  {
+		    add_state(current);
+		    process_link(t, tn, current, n, si);
+		  }
 	      }
 	    else
 	      {
-		process_link(t, tn, s->first, s->second, si);
+		if (ws)
+		  process_link(t, tn, s->first, s->second, si);
 		delete current;
 	      }
 	  }
@@ -80,6 +86,12 @@ namespace spot
     end();
   }
 
+  bool
+  tgba_reachable_iterator::want_state(const state*) const
+  {
+    return true;
+  }
+
   void
   tgba_reachable_iterator::start()
   {
diff --git a/src/tgbaalgos/reachiter.hh b/src/tgbaalgos/reachiter.hh
index 258fa57f2..afb2e31ff 100644
--- a/src/tgbaalgos/reachiter.hh
+++ b/src/tgbaalgos/reachiter.hh
@@ -1,4 +1,4 @@
-// Copyright (C) 2003, 2004, 2008  Laboratoire d'Informatique de Paris 6
+// Copyright (C) 2003, 2004, 2008, 2009  Laboratoire d'Informatique de Paris 6
 // (LIP6), département Systèmes Répartis Coopératifs (SRC), Université
 // Pierre et Marie Curie.
 //
@@ -56,6 +56,10 @@ namespace spot
     virtual const state* next_state() = 0;
     /// \}
 
+    /// Called by add_state or next_states implementations to filter
+    /// states.  Default implementation always return true.
+    virtual bool want_state(const state* s) const;
+
     /// Called by run() before starting its iteration.
     virtual void start();
     /// Called by run() once all states have been explored.