diff --git a/benedict/serializers/json.py b/benedict/serializers/json.py
index 72078fa..8cd61d4 100644
--- a/benedict/serializers/json.py
+++ b/benedict/serializers/json.py
@@ -3,6 +3,9 @@
 from __future__ import absolute_import
 
 from benedict.serializers.abstract import AbstractSerializer
+from benedict.utils import type_util
+
+from six import text_type
 
 import json
 
@@ -16,5 +19,18 @@ class JSONSerializer(AbstractSerializer):
 
     @staticmethod
     def encode(d, **kwargs):
+        kwargs.setdefault('default', JSONSerializer._encode_default)
         data = json.dumps(d, **kwargs)
         return data
+
+    @staticmethod
+    def _encode_default(obj):
+        if type_util.is_json_serializable(obj):
+            return None
+        elif type_util.is_set(obj):
+            return list(obj)
+        elif type_util.is_datetime(obj):
+            return obj.isoformat()
+        elif type_util.is_decimal(obj):
+            return text_type(obj)
+        return text_type(obj)
diff --git a/tests/core/test_dump.py b/tests/core/test_dump.py
index bfd18b1..7e92648 100644
--- a/tests/core/test_dump.py
+++ b/tests/core/test_dump.py
@@ -32,17 +32,24 @@ class dump_test_case(unittest.TestCase):
             'datetime': dt.datetime(2019, 6, 11),
         }
         r = """{
-    "datetime": "2019-06-11 00:00:00"
+    "datetime": "2019-06-11T00:00:00"
 }"""
         o = _dump(d)
         self.assertEqual(o, r)
 
-    def test_dump_with_decimal(self):
+    def test_dump_with_set(self):
         d = {
-            'decimal': Decimal('1.75'),
+            'set': set([0, 1, 2, 3, 4, 5]),
         }
         r = """{
-    "decimal": "1.75"
+    "set": [
+        0,
+        1,
+        2,
+        3,
+        4,
+        5
+    ]
 }"""
         o = _dump(d)
         self.assertEqual(o, r)
diff --git a/tests/dicts/test_benedict.py b/tests/dicts/test_benedict.py
index 9ebec1c..365d8c0 100644
--- a/tests/dicts/test_benedict.py
+++ b/tests/dicts/test_benedict.py
@@ -270,7 +270,7 @@ class benedict_test_case(unittest.TestCase):
         }
         b = benedict(d)
         expected_output = """{
-    "datetime": "2019-06-11 00:00:00"
+    "datetime": "2019-06-11T00:00:00"
 }"""
         output = b.dump()
         self.assertEqual(output, expected_output)