Index: libcxx/docs/Status/Cxx2bIssues.csv
===================================================================
--- libcxx/docs/Status/Cxx2bIssues.csv
+++ libcxx/docs/Status/Cxx2bIssues.csv
@@ -257,7 +257,7 @@
 "`3811 <https://wg21.link/LWG3811>`__","``views::as_const`` on ``ref_view<T>`` should return ``ref_view<const T>``","February 2023","","","|ranges|"
 "`3820 <https://wg21.link/LWG3820>`__","``cartesian_product_view::iterator::prev`` is not quite right","February 2023","","","|ranges|"
 "`3825 <https://wg21.link/LWG3825>`__","Missing compile-time argument ``id`` check in ``basic_format_parse_context::next_arg_id``","February 2023","","","|format|"
-"`3204 <https://wg21.link/LWG3204>`__","``sub_match::swap`` only swaps the base class","February 2023","","",""
+"`3204 <https://wg21.link/LWG3204>`__","``sub_match::swap`` only swaps the base class","February 2023","|Complete|","17.0",""
 "`3733 <https://wg21.link/LWG3733>`__","``ranges::to`` misuses ``cpp17-input-iterator``","February 2023","","","|ranges|"
 "`3742 <https://wg21.link/LWG3742>`__","``deque::prepend_range`` needs to permute","February 2023","","","|ranges|"
 "`3790 <https://wg21.link/LWG3790>`__","`P1467 <https://wg21.link/P1467>`__ accidentally changed ``nexttoward``'s signature","February 2023","","",""
Index: libcxx/include/regex
===================================================================
--- libcxx/include/regex
+++ libcxx/include/regex
@@ -225,6 +225,8 @@
     int compare(const sub_match& s) const;
     int compare(const string_type& s) const;
     int compare(const value_type* s) const;
+
+    void swap(sub_match& s) noexcept(see below);
 };
 
 typedef sub_match<const char*>             csub_match;
@@ -770,6 +772,7 @@
 #include <__iterator/wrap_iter.h>
 #include <__locale>
 #include <__memory_resource/polymorphic_allocator.h>
+#include <__type_traits/is_swappable.h>
 #include <__utility/move.h>
 #include <__utility/pair.h>
 #include <__utility/swap.h>
@@ -5008,6 +5011,16 @@
     _LIBCPP_INLINE_VISIBILITY
     int compare(const value_type* __s) const
         {return str().compare(__s);}
+
+    _LIBCPP_HIDE_FROM_ABI
+    void swap(sub_match& __s)
+#ifndef _LIBCPP_CXX03_LANG
+    _NOEXCEPT(__is_nothrow_swappable<_BidirectionalIterator>::value)
+#endif // _LIBCPP_CXX03_LANG
+    {
+        this->pair<_BidirectionalIterator, _BidirectionalIterator>::swap(__s);
+        std::swap(matched, __s.matched);
+    }
 };
 
 template <class _BiIter>
Index: libcxx/test/std/re/re.submatch/re.submatch.members/swap.pass.cpp
===================================================================
--- /dev/null
+++ libcxx/test/std/re/re.submatch/re.submatch.members/swap.pass.cpp
@@ -0,0 +1,77 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// <regex>
+
+// template <class BidirectionalIterator> class sub_match;
+
+// void swap(sub_match& s) noexcept(see below);
+
+#include <regex>
+#include <cassert>
+#include "test_macros.h"
+
+int main(int, char**)
+{
+    {
+        typedef char CharT;
+        typedef std::sub_match<const CharT*> SM;
+        const CharT s1[] = {'1', '2', '3', 0};
+        SM sm1;
+        sm1.first   = s1;
+        sm1.second  = s1+3;
+        sm1.matched = true;
+
+        SM sm2;
+        const CharT s2[] = {'c', 'a', 't', 0};
+        sm2.first   = s2;
+        sm2.second  = s2+3;
+        sm2.matched = false;
+
+        sm1.swap(sm2);
+
+        assert(sm1.first == s2);
+        assert(sm1.second == s2+3);
+        assert(!sm1.matched);
+
+        assert(sm2.first == s1);
+        assert(sm2.second == s1+3);
+        assert(sm2.matched);
+
+        ASSERT_NOEXCEPT(sm1.swap(sm2));
+    }
+#ifndef TEST_HAS_NO_WIDE_CHARACTERS
+    {
+        typedef wchar_t CharT;
+        typedef std::sub_match<const CharT*> SM;
+        const CharT s1[] = {L'1', L'2', L'3', 0};
+        SM sm1;
+        sm1.first   = s1;
+        sm1.second  = s1+3;
+        sm1.matched = true;
+
+        SM sm2;
+        const CharT s2[] = {L'c', L'a', L't', 0};
+        sm2.first   = s2;
+        sm2.second  = s2+3;
+        sm2.matched = false;
+
+        sm1.swap(sm2);
+
+        assert(sm1.first == s2);
+        assert(sm1.second == s2+3);
+        assert(!sm1.matched);
+
+        assert(sm2.first == s1);
+        assert(sm2.second == s1+3);
+        assert(sm2.matched);
+
+        ASSERT_NOEXCEPT(sm1.swap(sm2));
+    }
+#endif
+}