diff --git a/src/ltlvisit/apcollect.cc b/src/ltlvisit/apcollect.cc
index 1c4636f71..ab58a60bd 100644
--- a/src/ltlvisit/apcollect.cc
+++ b/src/ltlvisit/apcollect.cc
@@ -24,6 +24,8 @@
 
 #include "apcollect.hh"
 #include "ltlvisit/postfix.hh"
+#include "tgba/tgba.hh"
+#include "tgba/bdddict.hh"
 
 namespace spot
 {
@@ -63,6 +65,19 @@ namespace spot
       return s;
     }
 
+    bdd
+    atomic_prop_collect_as_bdd(const formula* f, tgba* a)
+    {
+      spot::ltl::atomic_prop_set aps;
+      atomic_prop_collect(f, &aps);
+      bdd_dict* d = a->get_dict();
+      bdd res = bddtrue;
+      for (atomic_prop_set::const_iterator i = aps.begin();
+	   i != aps.end(); ++i)
+	res &= bdd_ithvar(d->register_proposition(*i, a));
+      return res;
+    }
+
   }
 
 }
diff --git a/src/ltlvisit/apcollect.hh b/src/ltlvisit/apcollect.hh
index 3cf12f337..e8bc8d221 100644
--- a/src/ltlvisit/apcollect.hh
+++ b/src/ltlvisit/apcollect.hh
@@ -27,9 +27,12 @@
 
 #include <set>
 #include "ltlast/atomic_prop.hh"
+#include "bdd.h"
 
 namespace spot
 {
+  class tgba;
+
   namespace ltl
   {
     /// \addtogroup ltl_misc
@@ -50,6 +53,14 @@ namespace spot
     atomic_prop_set*
     atomic_prop_collect(const formula* f, atomic_prop_set* s = 0);
 
+    /// \brief Return the set of atomic propositions occurring in a formula, as a BDD.
+    ///
+    /// \param f the formula to inspect
+    /// \param a that automaton that should register the BDD variables used.
+    /// \return A conjunction the atomic propositions.
+    bdd
+    atomic_prop_collect_as_bdd(const formula* f, tgba* a);
+
     /// @}
   }
 }
diff --git a/src/tgbatest/ltl2tgba.cc b/src/tgbatest/ltl2tgba.cc
index a8138027b..ee5be9e7e 100644
--- a/src/tgbatest/ltl2tgba.cc
+++ b/src/tgbatest/ltl2tgba.cc
@@ -1101,18 +1101,7 @@ main(int argc, char** argv)
       //TA, STA, GTA, SGTA and TGTA
       if (ta_opt || tgta_opt)
         {
-          spot::ltl::atomic_prop_set* aps = atomic_prop_collect(f, 0);
-
-          bdd atomic_props_set_bdd = bddtrue;
-          for (spot::ltl::atomic_prop_set::const_iterator i = aps->begin(); i
-              != aps->end(); ++i)
-            {
-              bdd atomic_prop = bdd_ithvar((a->get_dict())->var_map[*i]);
-
-              atomic_props_set_bdd &= atomic_prop;
-
-            }
-          delete aps;
+	  bdd atomic_props_set_bdd = atomic_prop_collect_as_bdd(f, a);
 
           if (ta_opt)
             {