2 files changed, 20 insertions, 4 deletions
diff --git a/libstdc++-v3/include/std/iosfwd b/libstdc++-v3/include/std/iosfwd
index 2d79a131631..c8c67c86c3b 100644
--- a/libstdc++-v3/include/std/iosfwd
+++ b/libstdc++-v3/include/std/iosfwd
@@ -207,6 +207,24 @@ _GLIBCXX_END_NAMESPACE_CXX11
   /// Class for @c wchar_t mixed input and output file streams.
   typedef basic_fstream<wchar_t> 	wfstream;
 #endif
+
+#if __cplusplus >= 202002L && _GLIBCXX_USE_CXX11_ABI
+  template<typename _CharT, typename _Traits = char_traits<_CharT>,
+           typename _Allocator = allocator<_CharT>>
+    class basic_syncbuf;
+  template<typename _CharT, typename _Traits = char_traits<_CharT>,
+           typename _Allocator = allocator<_CharT>>
+    class basic_osyncstream;
+
+  using syncbuf = basic_syncbuf<char>;
+  using osyncstream = basic_osyncstream<char>;
+
+#ifdef _GLIBCXX_USE_WCHAR_T
+  using wsyncbuf = basic_syncbuf<wchar_t>;
+  using wosyncstream = basic_osyncstream<wchar_t>;
+#endif
+#endif // C++20 && CXX11_ABI
+
   /** @}  */
 
 _GLIBCXX_END_NAMESPACE_VERSION
diff --git a/libstdc++-v3/include/std/syncstream b/libstdc++-v3/include/std/syncstream
index 3cf2296f723..7a4f731ddd9 100644
--- a/libstdc++-v3/include/std/syncstream
+++ b/libstdc++-v3/include/std/syncstream
@@ -50,8 +50,7 @@ namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
-  template<typename _CharT, typename _Traits = char_traits<_CharT>,
-	    typename _Alloc = allocator<_CharT>>
+  template<typename _CharT, typename _Traits, typename _Alloc>
     class basic_syncbuf : public __syncbuf_base<_CharT, _Traits>
     {
     public:
@@ -241,8 +240,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       __mutex _M_mtx;
     };
 
-  template <typename _CharT, typename _Traits = char_traits<_CharT>,
-	    typename _Alloc = allocator<_CharT>>
+  template <typename _CharT, typename _Traits, typename _Alloc>
     class basic_osyncstream : public basic_ostream<_CharT, _Traits>
     {
       using __ostream_type = basic_ostream<_CharT, _Traits>;