diff --git a/NEWS b/NEWS
index 72817495d..be25f0deb 100644
--- a/NEWS
+++ b/NEWS
@@ -31,6 +31,8 @@ New in spot 2.1.2.dev (not yet released)
   * str_sere() and str_utf8_sere() were not returning the same
     string that print_sere() and print_utf8_sere() would print.
 
+  * Running the LTL parser in debug-mode would crash.
+
 New in spot 2.1.2 (2016-10-14)
 
   Command-line tools:
diff --git a/spot/parsetl/parsetl.yy b/spot/parsetl/parsetl.yy
index d4070e908..0830e70c7 100644
--- a/spot/parsetl/parsetl.yy
+++ b/spot/parsetl/parsetl.yy
@@ -236,8 +236,8 @@ using namespace spot;
 %destructor { $$->destroy(); } <ltl>
 
 %printer { debug_stream() << *$$; } <str>
-%printer { print_psl(debug_stream(), formula($$)); } <ltl>
-%printer { print_sere(debug_stream(), formula($$)); } sere bracedsere
+%printer { print_psl(debug_stream(), formula($$->clone())); } <ltl>
+%printer { print_sere(debug_stream(), formula($$->clone())); } sere bracedsere
 %printer { debug_stream() << $$; } <num>
 %printer { debug_stream() << $$.min << ".." << $$.max; } <minmax>
 
diff --git a/tests/core/parse.test b/tests/core/parse.test
index 48287dcd9..2a17a0582 100755
--- a/tests/core/parse.test
+++ b/tests/core/parse.test
@@ -1,7 +1,7 @@
 #! /bin/sh
 # -*- coding: utf-8 -*-
-# Copyright (C) 2009, 2010, 2011, 2012, 2013 Laboratoire de Recherche
-# et Développement de l'Epita (LRDE).
+# Copyright (C) 2009, 2010, 2011, 2012, 2013, 2016 Laboratoire de
+# Recherche et Développement de l'Epita (LRDE).
 # Copyright (C) 2003, 2004 Laboratoire d'Informatique de Paris 6 (LIP6),
 # département Systèmes Répartis Coopératifs (SRC), Université Pierre
 # et Marie Curie.
@@ -104,3 +104,6 @@ do
     fi
   fi
 done
+
+# Make sure running the parser in debug mode does not crash
+run 0 ../ikwiad -d 'a U b'