--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2011-08-31  Bruno Haible  <bruno@clisp.org>
+
+	freopen: Documentation.
+	* doc/posix-functions/freopen.texi: Document the bug with the NULL file
+	name.
+	Reported by Claudio Bley <claudio.bley@gmail.com>.
+
 2011-08-31  Claudio Bley  <claudio.bley@gmail.com>  (tiny change)
 
 	freopen: Don't crash if the filename argument is NULL.

--- a/doc/posix-functions/freopen.texi
+++ b/doc/posix-functions/freopen.texi
@@ -22,6 +22,10 @@
 On Windows platforms (excluding Cygwin), this function does not set @code{errno}
 upon failure.
 @item
+This function does not support a @code{NULL} file name argument on some
+platforms:
+OpenBSD 4.9, AIX 7.1, HP-UX 11.23, IRIX 6.5, OSF/1 5.1, Solaris 10, mingw.
+@item
 This function does not fail when the file name argument ends in a slash
 and (without the slash) names a nonexistent file or a file that is not a
 directory, on some platforms: