diff --git a/baselines/logger.py b/baselines/logger.py
index 4d9ffe6..36b0c98 100644
--- a/baselines/logger.py
+++ b/baselines/logger.py
@@ -92,7 +92,6 @@ class JSONOutputFormat(KVWriter):
     def writekvs(self, kvs):
         for k, v in sorted(kvs.items()):
             if hasattr(v, 'dtype'):
-                v = v.tolist()
                 kvs[k] = float(v)
         self.file.write(json.dumps(kvs) + '\n')
         self.file.flush()