diff --git a/ChangeLog b/ChangeLog
index 643459091..7882812f0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2004-05-14  Alexandre Duret-Lutz  <adl@src.lip6.fr>
 
+	* src/tgbaalgos/gtec/gtec.cc (emptiness_check::remove_component):
+	Do not try to erase state that are not found in H.
+	Report from Soheib Baarir.
+
 	* src/ltltest/reduc.test: Use ./defs and clean result.data.
 	* src/ltltest/Makefile.am (CLEANFILES): Clean result.data.
 
diff --git a/src/tgbaalgos/gtec/gtec.cc b/src/tgbaalgos/gtec/gtec.cc
index 1d8b147a0..1582f809c 100644
--- a/src/tgbaalgos/gtec/gtec.cc
+++ b/src/tgbaalgos/gtec/gtec.cc
@@ -64,7 +64,15 @@ namespace spot
 	  {
 	    state* s = i->current_state();
 	    numbered_state_heap::state_index_p spi = ecs_->h->index(s);
-	    assert(spi.second);
+
+	    // This state is not necessary in H, because if we were
+	    // doing inclusion checking during the emptiness-check
+	    // (redefining find()), the index `s' can be included in a
+	    // larger state and will not be found by index().  We can
+	    // safely ignore such states.
+	    if (!spi.first)
+	      continue;
+
 	    if (*spi.second != -1)
 	      {
 		*spi.second = -1;