diff --git a/xep-0155.xml b/xep-0155.xml
index b38158fa..5aed61cb 100644
--- a/xep-0155.xml
+++ b/xep-0155.xml
@@ -458,7 +458,7 @@ However, if the receiving party assumes that the other client will <em>not</em>
   <field
       var='language'
       type='list-single'
-      label='Primary written language of the chat (each value appears in order of preference and conforms to RFC 3066 and the IANA registry)'/>
+      label='Primary written language of the chat (each value appears in order of preference and conforms to RFC 4646 and the IANA registry)'/>
   <field
       var='otr'
       type='list-single'