--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2010-04-26  Jim Meyering  <jim@meyering.net>
+	    Bruno Haible  <bruno@clisp.org>
+
+	gnulib-common.m4: make glibc write diagnostics to stderr, not /dev/tty
+	* m4/gnulib-common.m4 (gl_COMMON_BODY): Set LIBC_FATAL_STDERR_.
+	Prompted by an exchange with Gilles Espinasse.
+
 2010-04-26  Jim Meyering  <meyering@redhat.com>
 
 	git-version-gen: aesthetic tweak

--- a/m4/gnulib-common.m4
+++ b/m4/gnulib-common.m4
@@ -1,4 +1,4 @@
-# gnulib-common.m4 serial 19
+# gnulib-common.m4 serial 20
 dnl Copyright (C) 2007-2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -35,6 +35,12 @@
    is a misnomer outside of parameter lists.  */
 #define _UNUSED_PARAMETER_ _GL_UNUSED
 ])
+  dnl Preparation for running test programs:
+  dnl Tell glibc to write diagnostics from -D_FORTIFY_SOURCE=2 to stderr, not
+  dnl to /dev/tty, so they can be redirected to log files.  Such diagnostics
+  dnl arise e.g., in the macros gl_PRINTF_DIRECTIVE_N, gl_SNPRINTF_DIRECTIVE_N.
+  LIBC_FATAL_STDERR_=1
+  export LIBC_FATAL_STDERR_
 ])
 
 # gl_MODULE_INDICATOR_CONDITION