diff --git a/Isosurfacing_3/include/CGAL/Isosurfacing_3/internal/marching_cubes_functors.h b/Isosurfacing_3/include/CGAL/Isosurfacing_3/internal/marching_cubes_functors.h
index b55407ffc28..96d679cd540 100644
--- a/Isosurfacing_3/include/CGAL/Isosurfacing_3/internal/marching_cubes_functors.h
+++ b/Isosurfacing_3/include/CGAL/Isosurfacing_3/internal/marching_cubes_functors.h
@@ -226,6 +226,9 @@ void triangles_to_polygon_soup(const TriangleRange& triangles,
 
         // simply use increasing indices
         polygons.push_back({id + 2, id + 1, id + 0});
+
+        // just a safeguard against arrays of the wrong size
+        CGAL_assertion(polygons.back().size() == 3);
       }
 
 #ifdef CGAL_LINKED_WITH_TBB
diff --git a/Isosurfacing_3/include/CGAL/Isosurfacing_3/internal/topologically_correct_marching_cubes_functors.h b/Isosurfacing_3/include/CGAL/Isosurfacing_3/internal/topologically_correct_marching_cubes_functors.h
index b1e0052c685..d2649a95bf5 100644
--- a/Isosurfacing_3/include/CGAL/Isosurfacing_3/internal/topologically_correct_marching_cubes_functors.h
+++ b/Isosurfacing_3/include/CGAL/Isosurfacing_3/internal/topologically_correct_marching_cubes_functors.h
@@ -198,6 +198,9 @@ public:
     points.insert(points.begin(), m_points.begin(), m_points.end());
     for (const auto& tri : m_triangles) {
       triangles.push_back({ tri[0], tri[1], tri[2] });
+
+      // just a safeguard against arrays of the wrong size
+      CGAL_assertion(triangles.back().size() == 3);
     }
   }