diff --git a/changelog.d/5500.bugfix b/changelog.d/5500.bugfix
new file mode 100644
index 0000000000..624c678435
--- /dev/null
+++ b/changelog.d/5500.bugfix
@@ -0,0 +1 @@
+Fix logging error when a tampered event is detected.
diff --git a/synapse/federation/federation_base.py b/synapse/federation/federation_base.py
index 58b929363f..1e925b19e7 100644
--- a/synapse/federation/federation_base.py
+++ b/synapse/federation/federation_base.py
@@ -163,7 +163,6 @@ class FederationBase(object):
                         logger.warning(
                             "Event %s content has been tampered, redacting",
                             pdu.event_id,
-                            pdu.get_pdu_json(),
                         )
                     return redacted_event