diff --git a/doc/doap.xml b/doc/doap.xml
index b43c4154a..79bf8a2ee 100644
--- a/doc/doap.xml
+++ b/doc/doap.xml
@@ -724,6 +724,15 @@
         <xmpp:note>refers to inclusion of delay stamp in presence</xmpp:note>
       </xmpp:SupportedXep>
     </implements>
+    <implements>
+      <xmpp:SupportedXep>
+        <xmpp:xep rdf:resource="https://xmpp.org/extensions/xep-0333.html"/>
+        <xmpp:version>1.0.0</xmpp:version>
+        <xmpp:since>0.10.0</xmpp:since>
+        <xmpp:status>partial</xmpp:status>
+        <xmpp:note>Used in mod_mam and mod_muc</xmpp:note>
+      </xmpp:SupportedXep>
+    </implements>
     <implements>
       <xmpp:SupportedXep>
         <xmpp:xep rdf:resource="https://xmpp.org/extensions/xep-0334.html"/>
diff --git a/plugins/mod_mam/mod_mam.lua b/plugins/mod_mam/mod_mam.lua
index ddceb0135..4eb49819e 100644
--- a/plugins/mod_mam/mod_mam.lua
+++ b/plugins/mod_mam/mod_mam.lua
@@ -364,7 +364,6 @@ local function should_store(stanza) --> boolean, reason: string
 		return true, "receipt";
 	end
 	if stanza:get_child(nil, "urn:xmpp:chat-markers:0") then
-		-- XXX Experimental XEP
 		return true, "marker";
 	end
 	if stanza:get_child("x", "jabber:x:conference")
diff --git a/plugins/muc/history.lib.lua b/plugins/muc/history.lib.lua
index 8d8fcf142..f85decfb9 100644
--- a/plugins/muc/history.lib.lua
+++ b/plugins/muc/history.lib.lua
@@ -218,7 +218,6 @@ module:hook("muc-message-is-historic", function (event)
 		return true, "encrypted";
 	end
 	if stanza:get_child(nil, "urn:xmpp:chat-markers:0") then
-		-- XXX Experimental XEP
 		return true, "marker";
 	end
 end, -1);