diff --git a/changelog.d/6278.bugfix b/changelog.d/6278.bugfix
new file mode 100644
index 0000000000..c107270461
--- /dev/null
+++ b/changelog.d/6278.bugfix
@@ -0,0 +1 @@
+Fix exception when remote servers attempt to join a room that they're not allowed to join.
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 488058fe68..2da520e6e8 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -1250,7 +1250,7 @@ class FederationHandler(BaseHandler):
                 builder=builder
             )
         except AuthError as e:
-            logger.warn("Failed to create join %r because %s", event, e)
+            logger.warn("Failed to create join to %s because %s", room_id, e)
             raise e
 
         event_allowed = yield self.third_party_event_rules.check_event_allowed(