diff --git a/include/boost/multi_array/iterator.hpp b/include/boost/multi_array/iterator.hpp
index 529d19e..c064c6f 100644
--- a/include/boost/multi_array/iterator.hpp
+++ b/include/boost/multi_array/iterator.hpp
@@ -97,7 +97,7 @@ public:
 
   template <class IteratorAdaptor, class DifferenceType>
   static void advance(IteratorAdaptor& x, DifferenceType n) {
-    x.idx_ += n;
+    x.base().idx_ += n;
   }
 
   template <class IteratorAdaptor1, class IteratorAdaptor2>