diff --git a/libstdc++-v3/include/bits/basic_string.tcc b/libstdc++-v3/include/bits/basic_string.tcc
index d8a279fc9ed..c759c2f9525 100644
--- a/libstdc++-v3/include/bits/basic_string.tcc
+++ b/libstdc++-v3/include/bits/basic_string.tcc
@@ -566,13 +566,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Operation>
     constexpr void
     basic_string<_CharT, _Traits, _Alloc>::
-    resize_and_overwrite(size_type __n, _Operation __op)
+    resize_and_overwrite(const size_type __n, _Operation __op)
     {
       const size_type __capacity = capacity();
       _CharT* __p;
       if (__n > __capacity)
 	{
-	  __p = _M_create(__n, __capacity);
+	  auto __new_capacity = __n; // Must not allow _M_create to modify __n.
+	  __p = _M_create(__new_capacity, __capacity);
 	  this->_S_copy(__p, _M_data(), length()); // exclude trailing null
 #if __cpp_lib_is_constant_evaluated
 	  if (std::is_constant_evaluated())
@@ -580,7 +581,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 	  _M_dispose();
 	  _M_data(__p);
-	  _M_capacity(__n);
+	  _M_capacity(__new_capacity);
 	}
       else
 	__p = _M_data();
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/capacity/char/resize_and_overwrite.cc b/libstdc++-v3/testsuite/21_strings/basic_string/capacity/char/resize_and_overwrite.cc
index f716030dad7..0ea5e2b10ef 100644
--- a/libstdc++-v3/testsuite/21_strings/basic_string/capacity/char/resize_and_overwrite.cc
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/capacity/char/resize_and_overwrite.cc
@@ -120,6 +120,26 @@ test05()
   return true;
 }
 
+void
+test06()
+{
+  std::string s = "0123456789";
+  s.resize_and_overwrite(16, [](char* p, int n) {
+    VERIFY( n == 16 );
+    std::char_traits<char>::copy(p + 10, "0123456798", 6);
+    return n;
+  });
+  VERIFY( s.size() == 16 );
+  VERIFY( s == "0123456789012345" );
+
+  s.resize_and_overwrite(4, [](char* p, int n) {
+    VERIFY( n == 4 );
+    std::char_traits<char>::copy(p, "abcd", 4);
+    return n;
+  });
+  VERIFY( s.size() == 4 );
+}
+
 int main()
 {
   test01();
@@ -127,4 +147,5 @@ int main()
   test03();
   test04();
   static_assert( test05() );
+  test06();
 }
diff --git a/libstdc++-v3/testsuite/std/format/functions/format.cc b/libstdc++-v3/testsuite/std/format/functions/format.cc
index 471cffb2b36..a8d5b652a5e 100644
--- a/libstdc++-v3/testsuite/std/format/functions/format.cc
+++ b/libstdc++-v3/testsuite/std/format/functions/format.cc
@@ -256,6 +256,11 @@ test_wchar()
   std::locale loc;
   s = std::format(loc, L"{:L} {:.3s}{:Lc}", true, L"data"sv, '.');
   VERIFY( s == L"true dat." );
+
+  s = std::format(L"{}", 0.0625);
+  VERIFY( s == L"0.0625" );
+  s = std::format(L"{}", 0.25);
+  VERIFY( s == L"0.25" );
 }
 
 void
diff --git a/libstdc++-v3/testsuite/std/format/functions/format_c++23.cc b/libstdc++-v3/testsuite/std/format/functions/format_c++23.cc
new file mode 100644
index 00000000000..f20c46cd7e3
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/format/functions/format_c++23.cc
@@ -0,0 +1,4 @@
+// { dg-do run { target c++23 } }
+// This test does not have -std=gnu++20 in dg-options so that format.cc
+// can be tested for e.g. -std=c++26
+#include "format.cc"