--- /dev/null
+// { dg-options "-std=gnu++20" }
+// { dg-do compile { target c++20 } }
+
+#include <iterator>
+
+struct InputIterator
+{
+ using difference_type = int;
+ using value_type = int;
+
+ constexpr int operator*() const noexcept { return 0; }
+ InputIterator& operator++() { return *this; }
+ constexpr void operator++(int) { }
+};
+
+static_assert( std::input_iterator<InputIterator> );
+static_assert( !std::forward_iterator<InputIterator> );
+
+constexpr bool
+test_lwg3643()
+{
+ std::counted_iterator<InputIterator> iter({}, 1);
+ iter++;
+ return iter == std::default_sentinel;
+}
+
+static_assert( test_lwg3643() );