diff --git a/language/predefined/closure/bindto.xml b/language/predefined/closure/bindto.xml
index 3e942e5b08..7f0056c835 100644
--- a/language/predefined/closure/bindto.xml
+++ b/language/predefined/closure/bindto.xml
@@ -76,6 +76,7 @@
       'static' to keep the current one. If an object is given, the type of the
       object will be used instead. This determines the visibility of protected
       and private methods of the bound object.
+      It is not allowed to pass (an object of) an internal class as this parameter.
      </para>
     </listitem>
    </varlistentry>