diff --git a/ChangeLog b/ChangeLog
index 887caccea..374af421d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2011-06-07  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
+
+	* src/ltltest/genltl.cc (X_n): Fix assertion.
+
 2011-06-06  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
 
 	* src/ltlvisit/dotty.cc (dotty_visitor): Reorder attributes.
diff --git a/src/ltltest/genltl.cc b/src/ltltest/genltl.cc
index 71bf0d086..2bc8f7290 100644
--- a/src/ltltest/genltl.cc
+++ b/src/ltltest/genltl.cc
@@ -420,7 +420,7 @@ formula* fair_response(std::string p, std::string q, std::string r, int n)
 // Builds X(X(...X(p))) with n occurrences of X.
 formula* X_n(formula* p, int n)
 {
-  assert(n > 0);
+  assert(n >= 0);
   formula* res = p;
   while (n--)
     res = X_(res);