diff --git a/synapse/rest/client/read_marker.py b/synapse/rest/client/read_marker.py
index d9ccd13e6..44e409b77 100644
--- a/synapse/rest/client/read_marker.py
+++ b/synapse/rest/client/read_marker.py
@@ -43,8 +43,6 @@ class ReadMarkerRestServlet(RestServlet):
         self._known_receipt_types = {ReceiptTypes.READ, ReceiptTypes.FULLY_READ}
         if hs.config.experimental.msc2285_enabled:
             self._known_receipt_types.add(ReceiptTypes.READ_PRIVATE)
-        self._known_receipt_types.add("com.beeper.read.extra")
-        self._known_receipt_types.add("com.beeper.fully_read.extra")
 
     async def on_POST(
         self, request: SynapseRequest, room_id: str