diff --git a/Nef_3/include/CGAL/Nef_3/SNC_indexed_items.h b/Nef_3/include/CGAL/Nef_3/SNC_indexed_items.h
index d9fb06512bd..6fae945cd02 100644
--- a/Nef_3/include/CGAL/Nef_3/SNC_indexed_items.h
+++ b/Nef_3/include/CGAL/Nef_3/SNC_indexed_items.h
@@ -20,6 +20,9 @@
 
 #ifndef CGAL_NEF_SNC_INDEXED_ITEMS_H
 #define CGAL_NEF_SNC_INDEXED_ITEMS_H
+
+#include <CGAL/atomic.h>
+
 #include <CGAL/Nef_3/Vertex.h>
 #include <CGAL/Nef_3/Halfedge.h>
 #include <CGAL/Nef_3/Halffacet.h>
@@ -39,7 +42,13 @@ class Index_generator {
  public:
   static int get_unique_index()
   {
-    static int unique = 0;
+    // initialized with 0
+    // http://en.cppreference.com/w/cpp/language/zero_initialization
+#ifdef CGAL_NO_ATOMIC
+    static int unique;
+#else
+    static CGAL::cpp11::atomic<int> unique;
+#endif
     return unique++;
   }
 };