diff --git a/gym/monitoring/monitor_manager.py b/gym/monitoring/monitor_manager.py
index b79153161..e53e32cf9 100644
--- a/gym/monitoring/monitor_manager.py
+++ b/gym/monitoring/monitor_manager.py
@@ -8,6 +8,7 @@ import six
 from gym import error, version
 from gym.monitoring import stats_recorder, video_recorder
 from gym.utils import atomic_write, closer
+from gym.utils.json_utils import json_encode_np
 
 logger = logging.getLogger(__name__)
 
@@ -180,7 +181,7 @@ class MonitorManager(object):
                 'videos': [(os.path.basename(v), os.path.basename(m))
                            for v, m in self.videos],
                 'env_info': self._env_info(),
-            }, f, default=json_encode)
+            }, f, default=json_encode_np)
 
     def close(self):
         """Flush all monitor data to disk and close any open rending windows."""
@@ -408,21 +409,3 @@ def collapse_env_infos(env_infos, training_dir):
         if key not in first:
             raise error.Error("env_info {} from training directory {} is missing expected key {}. This is unexpected and likely indicates a bug in gym.".format(first, training_dir, key))
     return first
-
-
-def json_encode(obj):
-    """
-    JSON can't serialize numpy types, so convert to pure python
-    """
-    if isinstance(obj, np.ndarray):
-        return list(obj)
-    elif isinstance(obj, np.float32):
-        return float(obj)
-    elif isinstance(obj, np.float64):
-        return float(obj)
-    elif isinstance(obj, np.int32):
-        return int(obj)
-    elif isinstance(obj, np.int64):
-        return int(obj)
-    else:
-        return obj
diff --git a/gym/monitoring/stats_recorder.py b/gym/monitoring/stats_recorder.py
index 44c87c87d..998c89b1b 100644
--- a/gym/monitoring/stats_recorder.py
+++ b/gym/monitoring/stats_recorder.py
@@ -4,6 +4,7 @@ import time
 
 from gym import error
 from gym.utils import atomic_write
+from gym.utils.json_utils import json_encode_np
 
 class StatsRecorder(object):
     def __init__(self, directory, file_prefix, autoreset=False, env_id=None):
@@ -99,4 +100,4 @@ class StatsRecorder(object):
                 'episode_lengths': self.episode_lengths,
                 'episode_rewards': self.episode_rewards,
                 'episode_types': self.episode_types,
-            }, f)
+            }, f, default=json_encode_np)
diff --git a/gym/utils/json_utils.py b/gym/utils/json_utils.py
new file mode 100644
index 000000000..6088d4ea9
--- /dev/null
+++ b/gym/utils/json_utils.py
@@ -0,0 +1,18 @@
+import numpy as np
+
+def json_encode_np(obj):
+    """
+    JSON can't serialize numpy types, so convert to pure python
+    """
+    if isinstance(obj, np.ndarray):
+        return list(obj)
+    elif isinstance(obj, np.float32):
+        return float(obj)
+    elif isinstance(obj, np.float64):
+        return float(obj)
+    elif isinstance(obj, np.int32):
+        return int(obj)
+    elif isinstance(obj, np.int64):
+        return int(obj)
+    else:
+        return obj