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diff --git a/boost/histogram/detail/iterator_adaptor.hpp b/boost/histogram/detail/iterator_adaptor.hpp
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+// Copyright 2019 Hans Dembinski
+//
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt
+// or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// Uses code segments from boost/iterator/iterator_adaptor.hpp
+// and boost/iterator/iterator_fascade.hpp
+
+#ifndef BOOST_HISTOGRAM_DETAIL_ITERATOR_ADAPTOR_HPP
+#define BOOST_HISTOGRAM_DETAIL_ITERATOR_ADAPTOR_HPP
+
+#include <iterator>
+#include <memory>
+#include <type_traits>
+#include <utility>
+
+namespace boost {
+namespace histogram {
+namespace detail {
+
+// operator->() needs special support for input iterators to strictly meet the
+// standard's requirements. If *i is not a reference type, we must still
+// produce an lvalue to which a pointer can be formed.  We do that by
+// returning a proxy object containing an instance of the reference object.
+template <class Reference>
+struct operator_arrow_dispatch_t // proxy references
+{
+  struct proxy {
+    explicit proxy(Reference const& x) noexcept : m_ref(x) {}
+    Reference* operator->() noexcept { return std::addressof(m_ref); }
+    Reference m_ref;
+  };
+
+  using result_type = proxy;
+  static result_type apply(Reference const& x) noexcept { return proxy(x); }
+};
+
+template <class T>
+struct operator_arrow_dispatch_t<T&> // "real" references
+{
+  using result_type = T*;
+  static result_type apply(T& x) noexcept { return std::addressof(x); }
+};
+
+// only for random access Base
+template <class Derived, class Base, class Reference = std::remove_pointer_t<Base>&,
+          class Value = std::decay_t<Reference>>
+class iterator_adaptor {
+  using operator_arrow_dispatch = operator_arrow_dispatch_t<Reference>;
+
+public:
+  using base_type = Base;
+
+  using reference = Reference;
+  using value_type = std::remove_const_t<Value>;
+  using pointer = typename operator_arrow_dispatch::result_type;
+  using difference_type = std::ptrdiff_t;
+  using iterator_category = std::random_access_iterator_tag;
+
+  iterator_adaptor() = default;
+
+  explicit iterator_adaptor(base_type const& iter) : iter_(iter) {}
+
+  pointer operator->() const noexcept {
+    return operator_arrow_dispatch::apply(this->derived().operator*());
+  }
+  reference operator[](difference_type n) const { return *(this->derived() + n); }
+
+  Derived& operator++() {
+    ++iter_;
+    return this->derived();
+  }
+
+  Derived& operator--() {
+    --iter_;
+    return this->derived();
+  }
+
+  Derived operator++(int) {
+    Derived tmp(this->derived());
+    ++iter_;
+    return tmp;
+  }
+
+  Derived operator--(int) {
+    Derived tmp(this->derived());
+    --iter_;
+    return tmp;
+  }
+
+  Derived& operator+=(difference_type n) {
+    iter_ += n;
+    return this->derived();
+  }
+
+  Derived& operator-=(difference_type n) {
+    iter_ -= n;
+    return this->derived();
+  }
+
+  Derived operator+(difference_type n) const {
+    Derived tmp(this->derived());
+    tmp += n;
+    return tmp;
+  }
+
+  Derived operator-(difference_type n) const { return operator+(-n); }
+
+  template <class... Ts>
+  difference_type operator-(const iterator_adaptor<Ts...>& x) const noexcept {
+    return iter_ - x.iter_;
+  }
+
+  template <class... Ts>
+  bool operator==(const iterator_adaptor<Ts...>& x) const noexcept {
+    return iter_ == x.iter_;
+  }
+  template <class... Ts>
+  bool operator!=(const iterator_adaptor<Ts...>& x) const noexcept {
+    return !this->derived().operator==(x); // equal operator may be overridden in derived
+  }
+  template <class... Ts>
+  bool operator<(const iterator_adaptor<Ts...>& x) const noexcept {
+    return iter_ < x.iter_;
+  }
+  template <class... Ts>
+  bool operator>(const iterator_adaptor<Ts...>& x) const noexcept {
+    return iter_ > x.iter_;
+  }
+  template <class... Ts>
+  bool operator<=(const iterator_adaptor<Ts...>& x) const noexcept {
+    return iter_ <= x.iter_;
+  }
+  template <class... Ts>
+  bool operator>=(const iterator_adaptor<Ts...>& x) const noexcept {
+    return iter_ >= x.iter_;
+  }
+
+  friend Derived operator+(difference_type n, const Derived& x) { return x + n; }
+
+  Base const& base() const noexcept { return iter_; }
+
+protected:
+  // for convenience in derived classes
+  using iterator_adaptor_ = iterator_adaptor;
+
+private:
+  Derived& derived() noexcept { return *static_cast<Derived*>(this); }
+  const Derived& derived() const noexcept { return *static_cast<Derived const*>(this); }
+
+  Base iter_;
+
+  template <class, class, class, class>
+  friend class iterator_adaptor;
+};
+
+} // namespace detail
+} // namespace histogram
+} // namespace boost
+
+#endif