diff --git a/Tetrahedral_remeshing/include/CGAL/Tetrahedral_remeshing/internal/tetrahedral_remeshing_helpers.h b/Tetrahedral_remeshing/include/CGAL/Tetrahedral_remeshing/internal/tetrahedral_remeshing_helpers.h
index 16b78ef265b..ea4d4a31fbf 100644
--- a/Tetrahedral_remeshing/include/CGAL/Tetrahedral_remeshing/internal/tetrahedral_remeshing_helpers.h
+++ b/Tetrahedral_remeshing/include/CGAL/Tetrahedral_remeshing/internal/tetrahedral_remeshing_helpers.h
@@ -792,6 +792,28 @@ bool is_edge_in_complex(const typename C3t3::Vertex_handle& v0,
     return false;
 }
 
+// this function is used in the demo plugin
+template<typename C3t3>
+bool protecting_balls_intersect(const typename C3t3::Edge& e,
+                                const C3t3& c3t3)
+{
+  const auto vv = c3t3.triangulation().vertices(e);
+  if(  c3t3.in_dimension(vv[0]) > 1
+    || c3t3.in_dimension(vv[1]) > 1)
+    return false;
+
+  const auto& p0 = vv[0]->point();
+  const auto& p1 = vv[1]->point();
+  if(p0.weight() == 0 || p1.weight() == 0)
+    return false;
+
+  const auto r0 = CGAL::approximate_sqrt(p0.weight());
+  const auto r1 = CGAL::approximate_sqrt(p1.weight());
+  const auto d = CGAL::approximate_sqrt(CGAL::squared_distance(p0, p1));
+
+  return d < r0 + r1;
+}
+
 template<typename C3t3, typename OutputIterator>
 OutputIterator incident_subdomains(const typename C3t3::Vertex_handle v,
                                    const C3t3& c3t3,