diff --git a/libcxx/include/__iterator/iterator_traits.h b/libcxx/include/__iterator/iterator_traits.h
--- a/libcxx/include/__iterator/iterator_traits.h
+++ b/libcxx/include/__iterator/iterator_traits.h
@@ -11,9 +11,9 @@
 #define _LIBCPP___ITERATOR_ITERATOR_TRAITS_H
 
 #include <__config>
-#include <concepts>
 #include <__iterator/incrementable_traits.h>
 #include <__iterator/readable_traits.h>
+#include <concepts>
 #include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -428,7 +428,7 @@
 
 template <class _Tp, class _Up, bool = __has_iterator_category<iterator_traits<_Tp> >::value>
 struct __has_iterator_category_convertible_to
-    : _BoolConstant<is_convertible<typename iterator_traits<_Tp>::iterator_category, _Up>::value>
+    : is_convertible<typename iterator_traits<_Tp>::iterator_category, _Up>
 {};
 
 template <class _Tp, class _Up>
@@ -436,7 +436,7 @@
 
 template <class _Tp, class _Up, bool = __has_iterator_concept<_Tp>::value>
 struct __has_iterator_concept_convertible_to
-    : _BoolConstant<is_convertible<typename _Tp::iterator_concept, _Up>::value>
+    : is_convertible<typename _Tp::iterator_concept, _Up>
 {};
 
 template <class _Tp, class _Up>
@@ -454,10 +454,11 @@
 template <class _Tp>
 struct __is_cpp17_random_access_iterator : public __has_iterator_category_convertible_to<_Tp, random_access_iterator_tag> {};
 
-// __is_cpp17_contiguous_iterator determines if an iterator is contiguous,
-// either because it advertises itself as such (in C++20) or because it
-// is a pointer type or a known trivial wrapper around a pointer type,
-// such as __wrap_iter<T*>.
+// __is_cpp17_contiguous_iterator determines if an iterator is known by
+// libc++ to be contiguous, either because it advertises itself as such
+// (in C++20) or because it is a pointer type or a known trivial wrapper
+// around a pointer type, such as __wrap_iter<T*>. Such iterators receive
+// special "contiguous" optimizations in std::copy and std::sort.
 //
 #if _LIBCPP_STD_VER > 17
 template <class _Tp>
diff --git a/libcxx/include/iterator b/libcxx/include/iterator
--- a/libcxx/include/iterator
+++ b/libcxx/include/iterator
@@ -1294,8 +1294,7 @@
     typedef typename iterator_traits<iterator_type>::reference         reference;
     typedef typename iterator_traits<iterator_type>::iterator_category iterator_category;
 #if _LIBCPP_STD_VER > 17
-    typedef _If<__is_cpp17_contiguous_iterator<_Iter>::value,
-                contiguous_iterator_tag, iterator_category>            iterator_concept;
+    typedef contiguous_iterator_tag                                    iterator_concept;
 #endif
 
 private:
@@ -1473,12 +1472,12 @@
 
 #if _LIBCPP_STD_VER <= 17
 template <class _It>
-struct __is_cpp17_contiguous_iterator<__wrap_iter<_It> > : __is_cpp17_contiguous_iterator<_It> {};
+struct __is_cpp17_contiguous_iterator<__wrap_iter<_It> > : true_type {};
 #endif
 
 template <class _Iter>
 _LIBCPP_CONSTEXPR
-_EnableIf<__is_cpp17_contiguous_iterator<_Iter>::value, decltype(_VSTD::__to_address(declval<_Iter>()))>
+decltype(_VSTD::__to_address(declval<_Iter>()))
 __to_address(__wrap_iter<_Iter> __w) _NOEXCEPT {
     return _VSTD::__to_address(__w.base());
 }
diff --git a/libcxx/test/libcxx/iterators/contiguous_iterators.pass.cpp b/libcxx/test/libcxx/iterators/contiguous_iterators.pass.cpp
--- a/libcxx/test/libcxx/iterators/contiguous_iterators.pass.cpp
+++ b/libcxx/test/libcxx/iterators/contiguous_iterators.pass.cpp
@@ -138,6 +138,21 @@
 };
 #endif
 
+struct fake_deque_iterator : std::deque<int>::iterator {
+    using element_type = int;
+};
+static_assert(std::__is_cpp17_random_access_iterator<fake_deque_iterator>::value, "");
+static_assert(!std::__is_cpp17_contiguous_iterator<fake_deque_iterator>::value, "");
+
+#if TEST_STD_VER >= 20
+struct fake2_deque_iterator : std::deque<int>::iterator {
+    using iterator_concept = std::contiguous_iterator_tag;
+    using element_type = int;
+};
+static_assert(std::__is_cpp17_random_access_iterator<fake2_deque_iterator>::value, "");
+static_assert(std::__is_cpp17_contiguous_iterator<fake2_deque_iterator>::value, "");
+#endif
+
 int main(int, char**)
 {
 //  basic tests
@@ -178,21 +193,19 @@
 
     static_assert(( std::__is_cpp17_contiguous_iterator<std::__wrap_iter<T *> >::value), "");
     static_assert(( std::__is_cpp17_contiguous_iterator<std::__wrap_iter<std::__wrap_iter<T *> > >::value), "");
-    static_assert((!std::__is_cpp17_contiguous_iterator<std::__wrap_iter<std::reverse_iterator<T *> > >::value), "");
 
-    static_assert((!std::__is_cpp17_contiguous_iterator<std::__wrap_iter<my_random_access_iterator> >::value), "");
-    static_assert((!std::__is_cpp17_contiguous_iterator<std::__wrap_iter<std::__wrap_iter<my_random_access_iterator> > >::value), "");
-    static_assert((!std::__is_cpp17_contiguous_iterator<std::__wrap_iter<std::reverse_iterator<my_random_access_iterator> > >::value), "");
+    // Here my_random_access_iterator is standing in for some user's fancy pointer type, written pre-C++20.
+    static_assert(( std::__is_cpp17_contiguous_iterator<std::__wrap_iter<my_random_access_iterator> >::value), "");
+    static_assert(( std::__is_cpp17_contiguous_iterator<std::__wrap_iter<std::__wrap_iter<my_random_access_iterator> > >::value), "");
 
 #if TEST_STD_VER >= 20
     static_assert(( std::__is_cpp17_contiguous_iterator<std::__wrap_iter<my_contiguous_iterator> >::value), "");
     static_assert(( std::__is_cpp17_contiguous_iterator<std::__wrap_iter<std::__wrap_iter<my_contiguous_iterator> > >::value), "");
-    static_assert((!std::__is_cpp17_contiguous_iterator<std::__wrap_iter<std::reverse_iterator<my_contiguous_iterator> > >::value), "");
 #endif
 
 //  iterators in the libc++ test suite
     static_assert((!std::__is_cpp17_contiguous_iterator<output_iterator       <char *> >::value), "");
-    static_assert((!std::__is_cpp17_contiguous_iterator<cpp17_input_iterator        <char *> >::value), "");
+    static_assert((!std::__is_cpp17_contiguous_iterator<cpp17_input_iterator  <char *> >::value), "");
     static_assert((!std::__is_cpp17_contiguous_iterator<forward_iterator      <char *> >::value), "");
     static_assert((!std::__is_cpp17_contiguous_iterator<bidirectional_iterator<char *> >::value), "");
     static_assert((!std::__is_cpp17_contiguous_iterator<random_access_iterator<char *> >::value), "");
@@ -228,14 +241,12 @@
     static_assert((!std::__is_cpp17_contiguous_iterator<std::deque<int>::const_iterator>             ::value), "");
     static_assert((!std::__is_cpp17_contiguous_iterator<std::deque<int>::reverse_iterator>           ::value), "");
     static_assert((!std::__is_cpp17_contiguous_iterator<std::deque<int>::const_reverse_iterator>     ::value), "");
-    static_assert((!std::__is_cpp17_contiguous_iterator<std::__wrap_iter<std::deque<int>::iterator> >::value), "");
 
 //  vector<bool> is random-access but not contiguous
     static_assert((!std::__is_cpp17_contiguous_iterator<std::vector<bool>::iterator>                   ::value), "");
     static_assert((!std::__is_cpp17_contiguous_iterator<std::vector<bool>::const_iterator>             ::value), "");
     static_assert((!std::__is_cpp17_contiguous_iterator<std::vector<bool>::reverse_iterator>           ::value), "");
     static_assert((!std::__is_cpp17_contiguous_iterator<std::vector<bool>::const_reverse_iterator>     ::value), "");
-    static_assert((!std::__is_cpp17_contiguous_iterator<std::__wrap_iter<std::vector<bool>::iterator> >::value), "");
 
 #if TEST_STD_VER >= 11
     static_assert(( std::__is_cpp17_contiguous_iterator<std::initializer_list<int>::iterator>      ::value), "");