diff --git a/libcxx/test/std/ranges/range.adaptors/range.join.view/iterator/ctor.default.pass.cpp b/libcxx/test/std/ranges/range.adaptors/range.join.view/iterator/ctor.default.pass.cpp
--- a/libcxx/test/std/ranges/range.adaptors/range.join.view/iterator/ctor.default.pass.cpp
+++ b/libcxx/test/std/ranges/range.adaptors/range.join.view/iterator/ctor.default.pass.cpp
@@ -23,16 +23,16 @@
   T *ptr_;
   constexpr DefaultCtorParent(T *ptr) : ptr_(ptr) {}
 
-  constexpr cpp17_input_iterator<T *> begin() { return cpp17_input_iterator<T *>(ptr_); }
-  constexpr cpp17_input_iterator<const T *> begin() const { return cpp17_input_iterator<const T *>(ptr_); }
+  constexpr forward_iterator<T *> begin() { return forward_iterator<T *>(ptr_); }
+  constexpr forward_iterator<const T *> begin() const { return forward_iterator<const T *>(ptr_); }
   constexpr T *end() { return ptr_ + 4; }
   constexpr const T *end() const { return ptr_ + 4; }
 };
 
 template<class T>
-constexpr bool operator==(const cpp17_input_iterator<T*> &lhs, const T *rhs) { return lhs.base() == rhs; }
+constexpr bool operator==(const forward_iterator<T*> &lhs, const T *rhs) { return lhs.base() == rhs; }
 template<class T>
-constexpr bool operator==(const T *lhs, const cpp17_input_iterator<T*> &rhs) { return rhs.base() == lhs; }
+constexpr bool operator==(const T *lhs, const forward_iterator<T*> &rhs) { return rhs.base() == lhs; }
 
 constexpr bool test() {
   using Base = DefaultCtorParent<ChildView>;
diff --git a/libcxx/test/std/ranges/range.adaptors/range.join.view/iterator/member_types.compile.pass.cpp b/libcxx/test/std/ranges/range.adaptors/range.join.view/iterator/member_types.compile.pass.cpp
--- a/libcxx/test/std/ranges/range.adaptors/range.join.view/iterator/member_types.compile.pass.cpp
+++ b/libcxx/test/std/ranges/range.adaptors/range.join.view/iterator/member_types.compile.pass.cpp
@@ -20,18 +20,18 @@
 
 template<class T>
 struct ForwardView : std::ranges::view_base {
-  friend forward_iterator<T*> begin(ForwardView&) { return forward_iterator<T*>(nullptr); }
-  friend forward_iterator<T*> begin(ForwardView const&) { return forward_iterator<T*>(nullptr); }
-  friend forward_iterator<T*> end(ForwardView&) { return forward_iterator<T*>(nullptr); }
-  friend forward_iterator<T*> end(ForwardView const&) { return forward_iterator<T*>(nullptr); }
+  friend forward_iterator<T*> begin(ForwardView&);
+  friend forward_iterator<T*> begin(ForwardView const&);
+  friend sentinel_wrapper<forward_iterator<T*>> end(ForwardView&);
+  friend sentinel_wrapper<forward_iterator<T*>> end(ForwardView const&);
 };
 
 template<class T>
 struct InputView : std::ranges::view_base {
-  friend cpp17_input_iterator<T*> begin(InputView&) { return cpp17_input_iterator<T*>(nullptr); }
-  friend cpp17_input_iterator<T*> begin(InputView const&) { return cpp17_input_iterator<T*>(nullptr); }
-  friend cpp17_input_iterator<T*> end(InputView&) { return cpp17_input_iterator<T*>(nullptr); }
-  friend cpp17_input_iterator<T*> end(InputView const&) { return cpp17_input_iterator<T*>(nullptr); }
+  friend cpp17_input_iterator<T*> begin(InputView&);
+  friend cpp17_input_iterator<T*> begin(InputView const&);
+  friend sentinel_wrapper<cpp17_input_iterator<T*>> end(InputView&);
+  friend sentinel_wrapper<cpp17_input_iterator<T*>> end(InputView const&);
 };
 
 template<class T>
diff --git a/libcxx/test/std/ranges/range.req/range.range/sentinel_t.compile.pass.cpp b/libcxx/test/std/ranges/range.req/range.range/sentinel_t.compile.pass.cpp
--- a/libcxx/test/std/ranges/range.req/range.range/sentinel_t.compile.pass.cpp
+++ b/libcxx/test/std/ranges/range.req/range.range/sentinel_t.compile.pass.cpp
@@ -25,6 +25,6 @@
 static_assert(std::same_as<std::ranges::sentinel_t<test_range<cpp20_input_iterator> >, sentinel>);
 static_assert(std::same_as<std::ranges::sentinel_t<test_range<cpp20_input_iterator> const>, sentinel>);
 static_assert(std::same_as<std::ranges::sentinel_t<test_non_const_range<cpp20_input_iterator> >, sentinel>);
-static_assert(std::same_as<std::ranges::sentinel_t<test_common_range<cpp17_input_iterator> >, cpp17_input_iterator<int*> >);
-static_assert(std::same_as<std::ranges::sentinel_t<test_common_range<cpp17_input_iterator> const>, cpp17_input_iterator<int const*> >);
-static_assert(std::same_as<std::ranges::sentinel_t<test_non_const_common_range<cpp17_input_iterator> >, cpp17_input_iterator<int*> >);
+static_assert(std::same_as<std::ranges::sentinel_t<test_common_range<forward_iterator> >, forward_iterator<int*> >);
+static_assert(std::same_as<std::ranges::sentinel_t<test_common_range<forward_iterator> const>, forward_iterator<int const*> >);
+static_assert(std::same_as<std::ranges::sentinel_t<test_non_const_common_range<forward_iterator> >, forward_iterator<int*> >);
diff --git a/libcxx/test/std/ranges/range.req/range.refinements/common_range.compile.pass.cpp b/libcxx/test/std/ranges/range.req/range.refinements/common_range.compile.pass.cpp
--- a/libcxx/test/std/ranges/range.req/range.refinements/common_range.compile.pass.cpp
+++ b/libcxx/test/std/ranges/range.req/range.refinements/common_range.compile.pass.cpp
@@ -26,11 +26,11 @@
 static_assert(!std::ranges::common_range<test_non_const_range<cpp17_input_iterator> >);
 static_assert(!std::ranges::common_range<test_non_const_range<cpp17_input_iterator> const>);
 
-static_assert(std::ranges::common_range<test_common_range<cpp17_input_iterator> >);
-static_assert(std::ranges::common_range<test_common_range<cpp17_input_iterator> const>);
+static_assert(std::ranges::common_range<test_common_range<forward_iterator> >);
+static_assert(std::ranges::common_range<test_common_range<forward_iterator> const>);
 
-static_assert(std::ranges::common_range<test_non_const_common_range<cpp17_input_iterator> >);
-static_assert(!std::ranges::common_range<test_non_const_common_range<cpp17_input_iterator> const>);
+static_assert(std::ranges::common_range<test_non_const_common_range<forward_iterator> >);
+static_assert(!std::ranges::common_range<test_non_const_common_range<forward_iterator> const>);
 
 struct subtly_not_common {
   int* begin() const;
diff --git a/libcxx/test/std/ranges/range.req/range.refinements/input_range.compile.pass.cpp b/libcxx/test/std/ranges/range.req/range.refinements/input_range.compile.pass.cpp
--- a/libcxx/test/std/ranges/range.req/range.refinements/input_range.compile.pass.cpp
+++ b/libcxx/test/std/ranges/range.req/range.refinements/input_range.compile.pass.cpp
@@ -32,14 +32,14 @@
 static_assert(!std::ranges::input_range<test_non_const_range<cpp17_input_iterator> const>);
 static_assert(!std::ranges::input_range<test_non_const_range<cpp20_input_iterator> const>);
 
-static_assert(std::ranges::input_range<test_common_range<cpp17_input_iterator> >);
+static_assert(std::ranges::input_range<test_common_range<forward_iterator> >);
 static_assert(!std::ranges::input_range<test_common_range<cpp20_input_iterator> >);
 
-static_assert(std::ranges::input_range<test_common_range<cpp17_input_iterator> const>);
+static_assert(std::ranges::input_range<test_common_range<forward_iterator> const>);
 static_assert(!std::ranges::input_range<test_common_range<cpp20_input_iterator> const>);
 
-static_assert(std::ranges::input_range<test_non_const_common_range<cpp17_input_iterator> >);
+static_assert(std::ranges::input_range<test_non_const_common_range<forward_iterator> >);
 static_assert(!std::ranges::input_range<test_non_const_common_range<cpp20_input_iterator> >);
 
-static_assert(!std::ranges::input_range<test_non_const_common_range<cpp17_input_iterator> const>);
+static_assert(!std::ranges::input_range<test_non_const_common_range<forward_iterator> const>);
 static_assert(!std::ranges::input_range<test_non_const_common_range<cpp20_input_iterator> const>);
diff --git a/libcxx/test/std/ranges/range.utility/range.subrange/advance.pass.cpp b/libcxx/test/std/ranges/range.utility/range.subrange/advance.pass.cpp
--- a/libcxx/test/std/ranges/range.utility/range.subrange/advance.pass.cpp
+++ b/libcxx/test/std/ranges/range.utility/range.subrange/advance.pass.cpp
@@ -31,7 +31,7 @@
   assert(a4.begin() == globalBuff + 4);
   assert(a4.size() == 4);
 
-  std::ranges::subrange<InputIter> b(InputIter(globalBuff), InputIter(globalBuff + 8));
+  std::ranges::subrange<InputIter, sentinel_wrapper<InputIter>> b(InputIter(globalBuff), sentinel_wrapper(InputIter(globalBuff + 8)));
   auto b1 = std::move(b).next();
   assert(b1.begin().base() == globalBuff + 1);
 
diff --git a/libcxx/test/support/test_iterators.h b/libcxx/test/support/test_iterators.h
--- a/libcxx/test/support/test_iterators.h
+++ b/libcxx/test/support/test_iterators.h
@@ -66,7 +66,6 @@
 
     TEST_CONSTEXPR_CXX14 It base() const {return it_;}
 
-    TEST_CONSTEXPR_CXX14 cpp17_input_iterator() : it_() {}
     explicit TEST_CONSTEXPR_CXX14 cpp17_input_iterator(It it) : it_(it) {}
     template <class U, class T>
         TEST_CONSTEXPR_CXX14 cpp17_input_iterator(const cpp17_input_iterator<U, T>& u) :it_(u.it_) {}
@@ -848,9 +847,22 @@
 template <std::input_or_output_iterator I>
 class sentinel_wrapper {
 public:
-    sentinel_wrapper() = default;
+    constexpr sentinel_wrapper() requires std::default_initializable<I> : base_() { }
+
+    // If the iterator itself is not default initializable (e.g. input iterators), we
+    // try to construct it from the base's iterator, which is sometimes default initializable.
+    constexpr sentinel_wrapper() requires (!std::default_initializable<I>)
+        : base_(decltype(std::declval<I>().base())())
+    { }
+
     constexpr explicit sentinel_wrapper(I base) : base_(std::move(base)) {}
 
+    sentinel_wrapper(sentinel_wrapper const&) = default;
+    sentinel_wrapper& operator=(sentinel_wrapper const&) = default;
+
+    sentinel_wrapper(sentinel_wrapper&&) = default;
+    sentinel_wrapper& operator=(sentinel_wrapper&&) = default;
+
     constexpr bool operator==(const I& other) const requires std::equality_comparable<I> {
         return base_ == other;
     }
@@ -865,7 +877,7 @@
     }
 
 private:
-    I base_ = I();
+    I base_;
 };
 
 template <std::input_or_output_iterator I>