diff --git a/src/ltlast/binop.cc b/src/ltlast/binop.cc
index c2866d4c3..e69c47f68 100644
--- a/src/ltlast/binop.cc
+++ b/src/ltlast/binop.cc
@@ -95,9 +95,9 @@ namespace spot
 	  is.sugar_free_boolean = false;
 	  is.in_nenoform = false;
 	  is.syntactic_safety =
-	    first->is_syntactic_obligation() && second->is_syntactic_safety();
-	  is.syntactic_obligation =
-	    first->is_syntactic_safety() && second->is_syntactic_obligation();
+	    first->is_syntactic_guarantee() && second->is_syntactic_safety();
+	  is.syntactic_guarantee =
+	    first->is_syntactic_safety() && second->is_syntactic_guarantee();
 	  // is.syntactic_obligation inherited
 	  is.syntactic_persistence = first->is_syntactic_recurrence()
 	    && second->is_syntactic_persistence();
diff --git a/src/ltltest/kind.test b/src/ltltest/kind.test
index 1211033e0..122364d95 100755
--- a/src/ltltest/kind.test
+++ b/src/ltltest/kind.test
@@ -1,5 +1,5 @@
 #! /bin/sh
-# Copyright (C) 2010, 2011 Laboratoire de Recherche et Developement to
+# Copyright (C) 2010, 2011, 2012 Laboratoire de Recherche et Developement to
 # l'Epita (LRDE).
 #
 # This file is part of Spot, a model checking library.
@@ -53,6 +53,11 @@ check 'a R (b R (c R d))' '&!xfLPsopr'
 check 'a U (b U (c U d))' '&!xfLPgopr'
 check 'a W (b W (c W d))' '&!xfLPsopr'
 check 'a M (b M (c M d))' '&!xfLPgopr'
+check 'Fa -> Fb'  'xLPopr'
+check 'Ga -> Fb'  'xLPgopr'
+check 'Fa -> Gb'  'xLPsopr'
+check '(Ga|Fc) -> Fb'  'xLPopr'
+check '(Ga|Fa) -> Gb'  'xLPopr'
 check '{a;c*;b}|->!Xb' '&fPsopr'
 check '{a;c*;b}|->X!b' '&!fPsopr'
 check '{a;c*;b}|->!Fb' '&xPsopr'