diff --git a/reference/mbstring/ini.xml b/reference/mbstring/ini.xml
index a8e7637cce..8602cc3dfa 100644
--- a/reference/mbstring/ini.xml
+++ b/reference/mbstring/ini.xml
@@ -189,6 +189,7 @@
     <listitem>
      <para>
       Defines character to substitute for invalid character encoding.
+      See <function>mb_substitute_character</function> for supported values.
      </para>
     </listitem>
    </varlistentry>