diff --git a/NEWS b/NEWS
index b53e5e23e..9e9755f1f 100644
--- a/NEWS
+++ b/NEWS
@@ -1,6 +1,8 @@
 New in spot 1.99.8a (not yet released)
 
-  Nothing yet.
+  Library:
+
+  * twa::ap_var() renamed to twa::ap_vars().
 
 New in spot 1.99.8 (2016-02-18)
 
diff --git a/spot/twa/twa.hh b/spot/twa/twa.hh
index 982196ed0..4745083cd 100644
--- a/spot/twa/twa.hh
+++ b/spot/twa/twa.hh
@@ -740,13 +740,13 @@ namespace spot
 
     /// \brief The vector of atomic propositions registered by this
     /// automaton.
-    const std::vector<formula>&  ap() const
+    const std::vector<formula>& ap() const
     {
       return aps_;
     }
 
     /// \brief The set of atomic propositions as a conjunction.
-    bdd ap_var() const
+    bdd ap_vars() const
     {
       return bddaps_;
     }
diff --git a/spot/twaalgos/stutter.cc b/spot/twaalgos/stutter.cc
index 288c696bb..d49a9e199 100644
--- a/spot/twaalgos/stutter.cc
+++ b/spot/twaalgos/stutter.cc
@@ -272,13 +272,13 @@ namespace spot
   twa_graph_ptr
   sl(const twa_graph_ptr& a)
   {
-    return sl(a, a->ap_var());
+    return sl(a, a->ap_vars());
   }
 
   twa_graph_ptr
   sl2(const twa_graph_ptr& a)
   {
-    return sl2(a, a->ap_var());
+    return sl2(a, a->ap_vars());
   }
 
   twa_graph_ptr
@@ -349,7 +349,7 @@ namespace spot
   sl2(twa_graph_ptr&& a, bdd atomic_propositions)
   {
     if (atomic_propositions == bddfalse)
-      atomic_propositions = a->ap_var();
+      atomic_propositions = a->ap_vars();
     unsigned num_states = a->num_states();
     unsigned num_edges = a->num_edges();
     std::vector<bdd> selfloops(num_states, bddfalse);
@@ -628,7 +628,7 @@ namespace spot
       }
 
     is_stut = is_stutter_invariant(make_twa_graph(aut, twa::prop_set::all()),
-				   std::move(neg), aut->ap_var());
+				   std::move(neg), aut->ap_vars());
     aut->prop_stutter_invariant(is_stut);
     return is_stut;
   }