diff --git a/STL_Extension/include/CGAL/utility.h b/STL_Extension/include/CGAL/utility.h
index 19860742748..6a766e8300c 100644
--- a/STL_Extension/include/CGAL/utility.h
+++ b/STL_Extension/include/CGAL/utility.h
@@ -158,6 +158,18 @@ operator==(const Quadruple<T1, T2, T3, T4>& x,
            (x.fourth == y.fourth) );
 }
 
+template <class T1, class T2, class T3, class T4>
+inline
+bool
+operator!=(const Quadruple<T1, T2, T3, T4>& x,
+           const Quadruple<T1, T2, T3, T4>& y)
+{
+  return ( (x.first == y.first) &&
+           (x.second == y.second) &&
+           (x.third == y.third) &&
+           (x.fourth == y.fourth) );
+}
+
 template <class T1, class T2, class T3, class T4>
 inline
 bool