diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 00d3c921cb07..2b5b3233e6e2 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,12 @@
+2000-05-08  Benjamin Kosnik  <bkoz@cygnus.com>
+
+	* bits/fstream.tcc (filebuf::_M_init_filebuf): Don't set
+	_M_buf_size based on macro, instead use _M_buf_size_opt.
+	* bits/std_streambuf.h (basic_streambuf): Add _M_buf_size_opt.
+	(basic_streambuf()): Set _M_buf_size_opt.
+	* testsuite/27_io/filebuf.cc (filebuf): Use _M_buf_size_opt
+	instead of _M_buf_size.
+
 2000-05-03  Phil Edwards  <pme@sourceware.cygnus.com>
             Felix Natter <fnatter@gmx.net>
 
diff --git a/libstdc++-v3/bits/fstream.tcc b/libstdc++-v3/bits/fstream.tcc
index d2d8c26c81c7..44cfb1901992 100644
--- a/libstdc++-v3/bits/fstream.tcc
+++ b/libstdc++-v3/bits/fstream.tcc
@@ -1,6 +1,6 @@
 // File based streams -*- C++ -*-
 
-// Copyright (C) 1997-1999 Free Software Foundation, Inc.
+// Copyright (C) 1997-1999, 2000 Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
 // software; you can redistribute it and/or modify it under the
@@ -42,7 +42,7 @@ namespace std
     _M_init_filebuf(void)
     {
       _M_buf_unified = true; // Tie input to output for basic_filebuf.
-      _M_buf_size = static_cast<int_type>(BUFSIZ * sizeof(char_type)); 
+      _M_buf_size = _M_buf_size_opt;
       try {
 	_M_file = new __file_type(&_M_lock);
       }
diff --git a/libstdc++-v3/bits/std_streambuf.h b/libstdc++-v3/bits/std_streambuf.h
index 6aa9204c5104..84699bfb0ab4 100644
--- a/libstdc++-v3/bits/std_streambuf.h
+++ b/libstdc++-v3/bits/std_streambuf.h
@@ -1,6 +1,6 @@
 // Stream buffer classes -*- C++ -*-
 
-// Copyright (C) 1997-1999 Free Software Foundation, Inc.
+// Copyright (C) 1997-1999, 2000 Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
 // software; you can redistribute it and/or modify it under the
@@ -84,9 +84,12 @@ namespace std {
       // leave it NULL.
       char_type*		_M_buf; 	
 
-      // Size of internal buffer, in bytes.
+      // Actual size of internal buffer, in bytes.
       int_type			_M_buf_size;
 
+      // Optimal or preferred size of internal buffer, in bytes.
+      int_type			_M_buf_size_opt;
+
       // True iff _M_in_* and _M_out_* buffers should always point to
       // the same place.  True for fstreams, false for sstreams.
       bool 			_M_buf_unified;	
@@ -284,10 +287,13 @@ namespace std {
 
     protected:
       basic_streambuf()
-      : _M_buf(NULL), _M_buf_size(0), _M_buf_unified(false),
-	_M_in_cur(0), _M_in_beg(0), _M_in_end(0), _M_out_cur(0), _M_out_beg(0),
-	_M_out_end(0), _M_mode(ios_base::openmode(0)), 
-	_M_locale_buf(locale()), _M_locale_set(false) 
+      : _M_buf(NULL), _M_buf_size(0), 
+	_M_buf_size_opt(static_cast<int_type>(BUFSIZ * sizeof(char_type))),
+	_M_buf_unified(false), _M_in_cur(0), _M_in_beg(0), _M_in_end(0), 
+	_M_out_cur(0), _M_out_beg(0), _M_out_end(0), 
+	_M_mode(ios_base::openmode(0)), _M_locale_buf(locale()), 
+	_M_locale_set(false) 
+
       { _M_fctype_buf =  &use_facet<__ctype_type>(this->getloc()); }
 
       // Get area:
diff --git a/libstdc++-v3/testsuite/27_io/filebuf.cc b/libstdc++-v3/testsuite/27_io/filebuf.cc
index 830e0b1ee584..586388e8e10b 100644
--- a/libstdc++-v3/testsuite/27_io/filebuf.cc
+++ b/libstdc++-v3/testsuite/27_io/filebuf.cc
@@ -1,6 +1,6 @@
 // 990117 bkoz test functionality of basic_filebuf for char_type == char
 
-// Copyright (C) 1997-1999 Free Software Foundation, Inc.
+// Copyright (C) 1997-1999, 2000 Free Software Foundation, Inc.
 //
 // This file is part of the GNU ISO C++ Library.  This library is free
 // software; you can redistribute it and/or modify it under the
@@ -37,7 +37,7 @@ class derived_filebuf: public std::filebuf
 {
  public:
   void
-  set_size(int_type __size) { _M_buf_size = __size; }
+  set_size(int_type __size) { _M_buf_size_opt = __size; }
 };
 
 derived_filebuf fb_01; // in