diff --git a/synapse/rest/client/v1/profile.py b/synapse/rest/client/v1/profile.py
index 6b379e4e5f..3218e47025 100644
--- a/synapse/rest/client/v1/profile.py
+++ b/synapse/rest/client/v1/profile.py
@@ -37,7 +37,7 @@ class ProfileDisplaynameRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_PUT(self, request, user_id):
-        auth_user, _, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request, allow_guest=True)
         user = UserID.from_string(user_id)
 
         try: