1 files changed, 5 insertions, 1 deletions
diff --git a/synapse/config/key.py b/synapse/config/key.py
index de964dff13..350ff1d665 100644
--- a/synapse/config/key.py
+++ b/synapse/config/key.py
@@ -404,7 +404,11 @@ def _parse_key_servers(key_servers, federation_verify_certificates):
     try:
         jsonschema.validate(key_servers, TRUSTED_KEY_SERVERS_SCHEMA)
     except jsonschema.ValidationError as e:
-        raise ConfigError("Unable to parse 'trusted_key_servers': " + e.message)
+        raise ConfigError(
+            "Unable to parse 'trusted_key_servers': {}".format(
+                e.message  # noqa: B306, jsonschema.ValidationError.message is a valid attribute
+            )
+        )
 
     for server in key_servers:
         server_name = server["server_name"]