diff --git a/resultsdb/messaging.py b/resultsdb/messaging.py
index 8dbbb40..f3c52ab 100644
--- a/resultsdb/messaging.py
+++ b/resultsdb/messaging.py
@@ -213,11 +213,12 @@ def __init__(self, **kwargs):
                 raise ValueError(f"Missing {attr!r} option for STOMP messaging plugin")
 
     def publish(self, msg):
-        msg = json.dumps(msg)
         # Add telemetry information. This includes an extra key
         # traceparent.
         TraceContextTextMapPropagator().inject(msg)
 
+        msg = json.dumps(msg)
+
         kwargs = dict(body=msg, headers={}, destination=self.destination)
 
         conn = stomp.connect.StompConnection11(**self.connection)