diff --git a/python/ray/rllib/agent.py b/python/ray/rllib/agent.py
index c71d8eb44..3cb850410 100644
--- a/python/ray/rllib/agent.py
+++ b/python/ray/rllib/agent.py
@@ -8,7 +8,7 @@ import os
 import pickle
 
 import tensorflow as tf
-from ray.tune.registry import ENV_CREATOR, get_registry
+from ray.tune.registry import ENV_CREATOR
 from ray.tune.result import TrainingResult
 from ray.tune.trainable import Trainable
 
@@ -63,7 +63,7 @@ class Agent(Trainable):
     _allow_unknown_subkeys = []
 
     def __init__(
-            self, config=None, env=None, registry=get_registry(),
+            self, config=None, env=None, registry=None,
             logger_creator=None):
         """Initialize an RLLib agent.
 
diff --git a/python/ray/tune/registry.py b/python/ray/tune/registry.py
index 3f53f7aad..71b532677 100644
--- a/python/ray/tune/registry.py
+++ b/python/ray/tune/registry.py
@@ -77,8 +77,8 @@ def _from_pinnable(obj):
 
 
 class _Registry(object):
-    def __init__(self, objs={}):
-        self._all_objects = objs
+    def __init__(self, objs=None):
+        self._all_objects = {} if objs is None else objs.copy()
         self._refs = []  # hard refs that prevent eviction of objects
 
     def register(self, category, key, value):