diff -rup a/manual/stdio.texi b/manual/stdio.texi
--- a/manual/stdio.texi	2012-01-01 05:16:32.000000000 -0700
+++ b/manual/stdio.texi	2012-02-09 23:46:31.660912211 -0700
@@ -2324,6 +2324,8 @@ the @var{size} argument specifies the ma
 produce.  The trailing null character is counted towards this limit, so
 you should allocate at least @var{size} characters for the string @var{s}.
 
+The trailing null byte is added to @var{s}, unless @var{size} is zero.
+
 The return value is the number of characters which would be generated
 for the given input, excluding the trailing null.  If this value is
 greater or equal to @var{size}, not all characters from the result have