diff --git a/functions/filesystem.xml b/functions/filesystem.xml
index b6753b15c0..15d1cb32ed 100644
--- a/functions/filesystem.xml
+++ b/functions/filesystem.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="iso-8859-1"?>
-<!-- $Revision: 1.98 $ -->
+<!-- $Revision: 1.99 $ -->
  <reference id="ref.filesystem">
   <title>Filesystem functions</title>
   <titleabbrev>Filesystem</titleabbrev>
@@ -1366,25 +1366,35 @@ $fp = fopen ("c:\\data\\info.txt", "r");
      </funcprototype>
     </funcsynopsis>
     <simpara>
-     Reads to EOF on the given file pointer and writes the results to
-     standard output.
+     Reads to EOF on the given file pointer from the current position and
+     writes the results to standard output.
     </simpara>
     <simpara>
      If an error occurs, <function>fpassthru</function> returns
      &false;.
     </simpara>
     <simpara>
-     The file pointer must be valid, and must point to a file
-     successfully opened by <function>fopen</function>,
-     <function>popen</function>, or <function>fsockopen</function>.
-     The file is closed when <function>fpassthru</function> is done
-     reading it (leaving <parameter>fp</parameter> useless).
+     The file pointer must be valid, and must point to a file successfully
+     opened by <function>fopen</function>, <function>popen</function>, or
+     <function>fsockopen</function>.  You may need to call
+     <function>rewind</function> to reset the file pointer to the beginning of
+     the file if you have already written data to the file.  The file is
+     closed when <function>fpassthru</function> is done reading it (leaving
+     <parameter>fp</parameter> useless).
     </simpara>
     <simpara>
      If you just want to dump the contents of a file to stdout you may
      want to use the <function>readfile</function>, which saves you
      the <function>fopen</function> call.
     </simpara>
+    <note>
+     <para>
+      When using <function>fpassthru</function> on a binary file on Windows
+      systems, you should make sure to open the file in binary mode by
+      appending a <literal>b</literal> to the mode used in the call to
+      <function>fopen</function>.
+     </para>
+    </note>
     <simpara>
      See also <function>readfile</function>,
      <function>fopen</function>, <function>popen</function>, and