diff --git a/ChangeLog b/ChangeLog
index 646c7184a0ab8324aff31499a91de3d41a514df1..130835ad5a80ed85b438ce84c914a8afafd6e134 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2011-01-17  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
+
+	Do not output empty parse error blocks in the CGI script.
+
+	* wrap/python/spot.i: Provide a __nonzero__() method for
+	parse_error_list.
+	* wrap/python/cgi-bin/ltl2tgba.in: Do not call format_parse_errors()
+	unconditionally.
+
 2011-01-12  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
 
 	Fix "unused function" warnings reported by clang++.
diff --git a/wrap/python/cgi-bin/ltl2tgba.in b/wrap/python/cgi-bin/ltl2tgba.in
index 173665cc6a839eb48ec21b963583018157b808d0..c0a7fad709358f6725a91c56807c230c0968d2ce 100755
--- a/wrap/python/cgi-bin/ltl2tgba.in
+++ b/wrap/python/cgi-bin/ltl2tgba.in
@@ -497,9 +497,10 @@ pel = spot.empty_parse_error_list()
 f = spot.parse(formula, pel, env, show_parse)
 if show_parse: print '</pre>'
 
-print '<font color="red"><pre>'
-err = spot.format_parse_errors(spot.get_cout(), formula, pel)
-print '</pre></font>'
+if pel:
+    print '<font color="red"><pre>'
+    err = spot.format_parse_errors(spot.get_cout(), formula, pel)
+    print '</pre></font>'
 
 if not f:
     print '<p><b>Aborting...</b></p>'
diff --git a/wrap/python/spot.i b/wrap/python/spot.i
index 5d44707e94b4a765432b231356bb4001da0d92aa..de4866e6240ab07048961982a39057f6c2f4130c 100644
--- a/wrap/python/spot.i
+++ b/wrap/python/spot.i
@@ -280,3 +280,13 @@ unblock_signal(int signum)
 }
 
 %}
+
+%extend spot::ltl::parse_error_list {
+
+bool
+__nonzero__()
+{
+  return !self->empty();
+}
+
+}