diff --git a/synapse/federation/sender/per_destination_queue.py b/synapse/federation/sender/per_destination_queue.py
index c83e1d4baf..80fbb9bd7f 100644
--- a/synapse/federation/sender/per_destination_queue.py
+++ b/synapse/federation/sender/per_destination_queue.py
@@ -232,7 +232,7 @@ class PerDestinationQueue(object):
                         # If there is no span context then we are either blacklisting
                         # this destination or we are not tracing
                         if not span_context == {}:
-                            if not "references" in span_context:
+                            if "references" not in span_context:
                                 span_context["references"] = [
                                     opentracing.active_span_context_as_string()
                                 ]