diff --git a/include/boost/iterator/iterator_adaptor.hpp b/include/boost/iterator/iterator_adaptor.hpp
index 50694a1..59ce07a 100644
--- a/include/boost/iterator/iterator_adaptor.hpp
+++ b/include/boost/iterator/iterator_adaptor.hpp
@@ -256,7 +256,7 @@ namespace boost
    public:
       iterator_adaptor() {}
 
-      explicit iterator_adaptor(Base iter)
+      explicit iterator_adaptor(Base const &iter)
           : m_iterator(iter)
       {
       }