diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index 3ab6cef9c2..1453ada8ed 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -179,6 +179,7 @@ class Auth(object):
     def get_public_keys(self, invite_event):
         return event_auth.get_public_keys(invite_event)
 
+    @opentracing.trace_deferred
     @defer.inlineCallbacks
     def get_user_by_req(
         self, request, allow_guest=False, rights="access", allow_expired=False