diff --git a/python/ray/rllib/agents/agent.py b/python/ray/rllib/agents/agent.py
index c082c1d28..0517e2b09 100644
--- a/python/ray/rllib/agents/agent.py
+++ b/python/ray/rllib/agents/agent.py
@@ -214,7 +214,7 @@ class Agent(Trainable):
         if logger_creator is None:
             timestr = datetime.today().strftime("%Y-%m-%d_%H-%M-%S")
             logdir_prefix = "{}_{}_{}".format(
-                [self._agent_name, self._env_id, timestr])
+                self._agent_name, self._env_id, timestr)
 
             def default_logger_creator(config):
                 """Creates a Unified logger with a default logdir prefix