diff --git a/src/ltltest/Makefile.am b/src/ltltest/Makefile.am
index 3b921a8e4..f6e0202e6 100644
--- a/src/ltltest/Makefile.am
+++ b/src/ltltest/Makefile.am
@@ -76,6 +76,7 @@ EXTRA_DIST = $(TESTS)
 
 # Ordered by strength of the test.  Test basic features first.
 TESTS = \
+  bare.test \
   parse.test \
   parseerr.test \
   utf8.test \
diff --git a/src/ltltest/bare.test b/src/ltltest/bare.test
new file mode 100755
index 000000000..7395a067c
--- /dev/null
+++ b/src/ltltest/bare.test
@@ -0,0 +1,33 @@
+#!/bin/sh
+# -*- coding: utf-8 -*-
+# Copyright (C) 2012 Laboratoire de Recherche et Développement
+# de l'Epita (LRDE).
+#
+# This file is part of Spot, a model checking library.
+#
+# Spot is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# Spot is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+# License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. ./defs
+set -e
+
+test "`../../bin/ltlfilt -p -f 'GFP_0.b_c'`" = "(G(F(P_0.b_c)))"
+test "`../../bin/ltlfilt -f 'GFP_0.b_c'`" = "GFP_0.b_c"
+foo=`../../bin/ltlfilt -p -f 'GF"P_0.b_c"'`
+test "$foo" = "(G(F(P_0.b_c)))"
+
+foo=`../../bin/ltlfilt -p -f '"a.b" U c.d.e'`
+test "$foo" = "(a.b) U (c.d.e)"
+
+foo=`../../bin/ltlfilt -f '"a.b" U c.d.e'`
+test "$foo" = "a.b U c.d.e"
diff --git a/src/ltlvisit/tostring.cc b/src/ltlvisit/tostring.cc
index e2d6b92a0..ada53b33f 100644
--- a/src/ltlvisit/tostring.cc
+++ b/src/ltlvisit/tostring.cc
@@ -198,13 +198,13 @@ namespace spot
 	    || *str == 'F'
 	    || *str == 'G'
 	    || *str == 'X'
-	    || !(isalpha(*str) || *str == '_')
+	    || !(isalpha(*str) || *str == '_' || *str == '.')
 	    || !strcasecmp(str, "true")
 	    || !strcasecmp(str, "false"))
 	  return false;
 	// The remaining of the word must be alphanumeric.
 	while (*++str)
-	  if (!(isalnum(*str) || *str == '_'))
+	  if (!(isalnum(*str) || *str == '_' || *str == '.'))
 	    return false;
 	return true;
       }