diff --git a/src/polymesh/algorithms/normal_estimation.hh b/src/polymesh/algorithms/normal_estimation.hh
index 21464054b302f5ccdfc8244d8b3e73a216b29b32..a1f3bd19b68f2abb37d4fb1f2f0f38663002ff04 100644
--- a/src/polymesh/algorithms/normal_estimation.hh
+++ b/src/polymesh/algorithms/normal_estimation.hh
@@ -19,35 +19,41 @@ template <class Vec3, class IsHardEdgeF>
 
     auto const hard_edges = m.edges().map([&](edge_handle e) { return e.is_boundary() ? true : is_hard_edge(e); });
 
-    return m.halfedges().map([&](halfedge_handle h) {
-        Vec3 n = face_normals[h.face()];
+    return m.halfedges().map(
+        [&](halfedge_handle h)
+        {
+            if (h.is_boundary())
+                return Vec3{};
 
-        auto h0 = h;
-        auto h1 = h.next().opposite();
+            POLYMESH_ASSERT(h.face().is_valid());
+            Vec3 n = face_normals[h.face()];
 
-        // iterate over h0
-        auto hh = h0;
-        while (hh != h1 && !hard_edges[hh])
-        {
-            hh = hh.opposite().prev();
-            n += face_normals[hh.face()];
-        }
+            auto h0 = h;
+            auto h1 = h.next().opposite();
 
-        // iterate over h1 if not reached around
-        if (hh != h1)
-        {
-            hh = h1;
-            while (hh != h0 && !hard_edges[hh])
+            // iterate over h0
+            auto hh = h0;
+            while (hh != h1 && !hard_edges[hh])
             {
+                hh = hh.opposite().prev();
                 n += face_normals[hh.face()];
-                hh = hh.next().opposite();
             }
-        }
 
-        // normalize
-        auto l = std::sqrt(n.x * n.x + n.y * n.y + n.z * n.z);
-        return n / (l + 1e-30f);
-    });
+            // iterate over h1 if not reached around
+            if (hh != h1)
+            {
+                hh = h1;
+                while (hh != h0 && !hard_edges[hh])
+                {
+                    n += face_normals[hh.face()];
+                    hh = hh.next().opposite();
+                }
+            }
+
+            // normalize
+            auto l = std::sqrt(n.x * n.x + n.y * n.y + n.z * n.z);
+            return n / (l + 1e-30f);
+        });
 }
 
 /// same as normal_estimation(face_attribute<Vec3>, ...)
diff --git a/src/polymesh/attributes.hh b/src/polymesh/attributes.hh
index ffb4921569d24f527b7800c0d219bdeed3d853c4..58eb48a34a3739b4f25966e3849a880d96952ad6 100644
--- a/src/polymesh/attributes.hh
+++ b/src/polymesh/attributes.hh
@@ -247,4 +247,80 @@ auto attribute(Collection const& c, AttrT const& defaultValue = {}) -> decltype(
     return c.make_attribute(defaultValue);
 }
 
+namespace detail
+{
+template <class T>
+struct is_mesh_attribute_t : std::false_type
+{
+};
+template <class T>
+struct is_mesh_attribute_t<vertex_attribute<T>> : std::true_type
+{
+};
+template <class T>
+struct is_mesh_attribute_t<edge_attribute<T>> : std::true_type
+{
+};
+template <class T>
+struct is_mesh_attribute_t<halfedge_attribute<T>> : std::true_type
+{
+};
+template <class T>
+struct is_mesh_attribute_t<face_attribute<T>> : std::true_type
+{
+};
+template <class tag, class T>
+struct is_mesh_attribute_t<primitive_attribute<tag, T>> : std::true_type
+{
+};
+	
+template <class T>
+struct is_vertex_attribute_t : std::false_type
+{
+};
+template <class T>
+struct is_vertex_attribute_t<vertex_attribute<T>> : std::true_type
+{
+};
+	
+template <class T>
+struct is_face_attribute_t : std::false_type
+{
+};
+template <class T>
+struct is_face_attribute_t<face_attribute<T>> : std::true_type
+{
+};
+	
+template <class T>
+struct is_edge_attribute_t : std::false_type
+{
+};
+template <class T>
+struct is_edge_attribute_t<edge_attribute<T>> : std::true_type
+{
+};
+	
+template <class T>
+struct is_halfedge_attribute_t : std::false_type
+{
+};
+template <class T>
+struct is_halfedge_attribute_t<halfedge_attribute<T>> : std::true_type
+{
+};
+}
+
+/// true iff (decayed) T is vertex, face, edge, or halfedge attribute
+template <class T>
+constexpr bool is_mesh_attribute = detail::is_mesh_attribute_t<std::decay_t<T>>::value;
+template <class T>
+constexpr bool is_vertex_attribute = detail::is_vertex_attribute_t<std::decay_t<T>>::value;
+template <class T>
+constexpr bool is_face_attribute = detail::is_face_attribute_t<std::decay_t<T>>::value;
+template <class T>
+constexpr bool is_edge_attribute = detail::is_edge_attribute_t<std::decay_t<T>>::value;
+template <class T>
+constexpr bool is_halfedge_attribute = detail::is_halfedge_attribute_t<std::decay_t<T>>::value;
+
 } // namespace polymesh