diff --git a/appendices/ini.xml b/appendices/ini.xml
index d57bba536b..07165c1666 100644
--- a/appendices/ini.xml
+++ b/appendices/ini.xml
@@ -5230,6 +5230,13 @@ include_path=".;c:\php\includes"
         file upload. Must be writable by whatever user PHP
         is running as. If not specified PHP will use the system's default.
        </para>
+       <para>
+        If the directory specified here is not wriable, PHP falls back to 
+        the system defeault temporary directory. If 
+        <link linkend="ini.open-basedir">open_basedir</link> is on, then 
+        the system default directory must be allowed for an upload to 
+        succeed.
+       </para>
       </listitem>
      </varlistentry>