diff --git a/ChangeLog b/ChangeLog
index 393311174d..acf97b2f98 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
 2005-01-05  Ulrich Drepper  <drepper@redhat.com>
 
+	* libio/iofopncook.c (_IO_cookie_seekoff): Define.  Mark offset as
+	invalid to disable optimizations in fileops which won't work here.
+	(_IO_cookie_jumps): Use it.
+	(_IO_old_cookie_jumps): Likewise.
+	* libio/fmemopen.c (fmemopen_seek): Result must be returned in *P,
+	not the return value.
+	* stdio-common/Makefile (tests): Add tst-fmemopen2.
+	* stdio-common/tst-fmemopen2.c: New file.
+
 	* sysdeps/unix/sysv/linux/bits/waitflags.h: Define __WNOTHREAD.
 
 2005-01-05  Roland McGrath  <roland@redhat.com>
diff --git a/libio/fmemopen.c b/libio/fmemopen.c
index ab6ffdd678..265b848ebe 100644
--- a/libio/fmemopen.c
+++ b/libio/fmemopen.c
@@ -1,5 +1,5 @@
 /* Fmemopen implementation.
-   Copyright (C) 2000, 2002 Free Software Foundation, Inc.
+   Copyright (C) 2000, 2002, 2005 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by  Hanno Mueller, kontakt@hanno.de, 2000.
 
@@ -27,8 +27,6 @@
  * but couldn't find it in libio. The following snippet of code is an
  * attempt to implement what glibc's documentation describes.
  *
- * No, it isn't really tested yet. :-)
- *
  *
  *
  * I already see some potential problems:
@@ -176,9 +174,9 @@ fmemopen_seek (void *cookie, _IO_off64_t *p, int w)
   if (np < 0 || (size_t) np > c->size)
     return -1;
 
-  c->pos = np;
+  *p = c->pos = np;
 
-  return np;
+  return 0;
 }
 
 
diff --git a/libio/iofopncook.c b/libio/iofopncook.c
index 321eb67b8d..eba3d435dc 100644
--- a/libio/iofopncook.c
+++ b/libio/iofopncook.c
@@ -1,4 +1,5 @@
-/* Copyright (C) 1993,95,97,99,2000,2002,2004 Free Software Foundation, Inc.
+/* Copyright (C) 1993,95,97,99,2000,2002,2004, 2005
+   Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -94,6 +95,20 @@ _IO_cookie_close (fp)
 }
 
 
+static _IO_off64_t
+_IO_cookie_seekoff (fp, offset, dir, mode)
+     _IO_FILE *fp;
+     _IO_off64_t offset;
+     int dir;
+     int mode;
+{
+  /* We must force the fileops code to always use seek to determine
+     the position.  */
+  fp->_offset = _IO_pos_BAD;
+  return INTUSE(_IO_file_seekoff) (fp, offset, dir, mode);
+}
+
+
 static const struct _IO_jump_t _IO_cookie_jumps = {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, INTUSE(_IO_file_finish)),
@@ -103,7 +118,7 @@ static const struct _IO_jump_t _IO_cookie_jumps = {
   JUMP_INIT(pbackfail, INTUSE(_IO_default_pbackfail)),
   JUMP_INIT(xsputn, INTUSE(_IO_file_xsputn)),
   JUMP_INIT(xsgetn, INTUSE(_IO_default_xsgetn)),
-  JUMP_INIT(seekoff, INTUSE(_IO_file_seekoff)),
+  JUMP_INIT(seekoff, _IO_cookie_seekoff),
   JUMP_INIT(seekpos, _IO_default_seekpos),
   JUMP_INIT(setbuf, INTUSE(_IO_file_setbuf)),
   JUMP_INIT(sync, INTUSE(_IO_file_sync)),
@@ -223,7 +238,7 @@ static const struct _IO_jump_t _IO_old_cookie_jumps = {
   JUMP_INIT(pbackfail, INTUSE(_IO_default_pbackfail)),
   JUMP_INIT(xsputn, INTUSE(_IO_file_xsputn)),
   JUMP_INIT(xsgetn, INTUSE(_IO_default_xsgetn)),
-  JUMP_INIT(seekoff, INTUSE(_IO_file_seekoff)),
+  JUMP_INIT(seekoff, _IO_cookie_seekoff),
   JUMP_INIT(seekpos, _IO_default_seekpos),
   JUMP_INIT(setbuf, INTUSE(_IO_file_setbuf)),
   JUMP_INIT(sync, INTUSE(_IO_file_sync)),
diff --git a/stdio-common/Makefile b/stdio-common/Makefile
index 3a66f1d021..2e797e4dfe 100644
--- a/stdio-common/Makefile
+++ b/stdio-common/Makefile
@@ -1,4 +1,4 @@
-# Copyright (C) 1991-2002, 2003, 2004 Free Software Foundation, Inc.
+# Copyright (C) 1991-2002, 2003, 2004, 2005 Free Software Foundation, Inc.
 # This file is part of the GNU C Library.
 
 # The GNU C Library is free software; you can redistribute it and/or
@@ -53,7 +53,7 @@ tests := tstscanf test_rdwr test-popen tstgetln test-fseek \
 	 scanf11 scanf12 tst-tmpnam tst-cookie tst-obprintf tst-sscanf \
 	 tst-swprintf tst-fseek tst-fmemopen test-vfprintf tst-gets \
 	 tst-perror tst-sprintf tst-rndseek tst-fdopen tst-fphex bug14 bug15 \
-	 tst-popen tst-unlockedio
+	 tst-popen tst-unlockedio tst-fmemopen2
 
 test-srcs = tst-unbputc tst-printf