diff --git a/ChangeLog b/ChangeLog
index d7824302f..3f8e4b637 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2003-08-25  Alexandre Duret-Lutz  <aduret@src.lip6.fr>
+
+	* src/tgba/state.hh (state_ptr_less_than): Make sure left is
+	non-null.  Suggested by Denis Poitreneaud.
+
 2003-08-23  Alexandre Duret-Lutz  <aduret@src.lip6.fr>
 
 	* wrap/python/Makefile.am (MAINTAINERCLEANFILES): Add
diff --git a/src/tgba/state.hh b/src/tgba/state.hh
index c989c50e9..9584f94de 100644
--- a/src/tgba/state.hh
+++ b/src/tgba/state.hh
@@ -46,6 +46,7 @@ namespace spot
     bool
     operator()(const state* left, const state* right) const
     {
+      assert(left);
       return left->compare(right) < 0;
     }
   };