--- a/libstdc++-v3/src/c++17/floating_from_chars.cc
+++ b/libstdc++-v3/src/c++17/floating_from_chars.cc
@@ -495,10 +495,16 @@
 from_chars(const char* first, const char* last, __ieee128& value,
          chars_format fmt) noexcept
 {
+  errc ec = errc::invalid_argument;
+#if _GLIBCXX_USE_CXX11_ABI
   buffer_resource mr;
   pmr::string buf(&mr);
+#else
+  string buf;
+  if (!reserve_string(buf))
+    return make_result(first, 0, {}, ec);
+#endif
   size_t len = 0;
-  errc ec = errc::invalid_argument;
   __try
     {
       if (const char* pat = pattern(first, last, fmt, buf)) [[likely]]