diff --git a/.travis.yml b/.travis.yml
index 63470eee..cc7cd4d6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -17,8 +17,8 @@ install:
   - pip install $DJANGO
   - python setup.py -q develop
   - pip install -r requirements-test.txt
-  # Temporary
-  - pip install --upgrade https://github.com/openwisp/netdiff/tarball/issue/39-detect-node-changes
+  # Temporary, remove when netdiff 0.8.0 is released
+  - pip install --upgrade https://github.com/openwisp/netdiff/tarball/master
 
 script:
   - coverage run --source=openwisp_network_topology runtests.py
diff --git a/openwisp_network_topology/base/node.py b/openwisp_network_topology/base/node.py
index 5d34604e..14c94ca8 100644
--- a/openwisp_network_topology/base/node.py
+++ b/openwisp_network_topology/base/node.py
@@ -70,8 +70,8 @@ def json(self, dict=False, **kwargs):
             value = getattr(self, attr)
             if value or attr == 'properties':
                 netjson[attr] = value
-        netjson['properties']['created'] = self.created
-        netjson['properties']['modified'] = self.modified
+        netjson['properties']['created'] = JSONEncoder().default(self.created)
+        netjson['properties']['modified'] = JSONEncoder().default(self.modified)
         if dict:
             return netjson
         return json.dumps(netjson, cls=JSONEncoder, **kwargs)
diff --git a/openwisp_network_topology/tests/test_node.py b/openwisp_network_topology/tests/test_node.py
index 1b261b4c..d147da9a 100644
--- a/openwisp_network_topology/tests/test_node.py
+++ b/openwisp_network_topology/tests/test_node.py
@@ -1,5 +1,6 @@
 import swapper
 from django.test import TestCase
+from rest_framework.utils.encoders import JSONEncoder
 
 from .utils import CreateGraphObjectsMixin, CreateOrgMixin
 
@@ -89,8 +90,8 @@ def test_json(self):
                 'local_addresses': ['10.0.0.1'],
                 'properties': {
                     'gateway': True,
-                    'created': n.created,
-                    'modified': n.modified,
+                    'created': JSONEncoder().default(n.created),
+                    'modified': JSONEncoder().default(n.modified),
                 },
             },
         )
diff --git a/openwisp_network_topology/tests/test_topology.py b/openwisp_network_topology/tests/test_topology.py
index 7b5702cf..a229691d 100644
--- a/openwisp_network_topology/tests/test_topology.py
+++ b/openwisp_network_topology/tests/test_topology.py
@@ -211,7 +211,9 @@ def test_update_changed(self):
         self.assertEqual(link.properties, {'pretty': True})
         self.assertEqual(link.cost, 1.5)
         self.assertEqual(link.cost_text, '15 Mbps')
-        link = self.link_model.objects.last()
+        link = self.link_model.get_from_nodes(
+            source='192.168.0.1', target='192.168.0.3', topology=t
+        )
         self.assertEqual(link.properties, {'pretty': False})
         self.assertEqual(link.cost, 2.0)
         self.assertEqual(link.cost_text, '20 Mbps')
diff --git a/tests/openwisp2/sample_network_topology/migrations/0002_json_properties.py b/tests/openwisp2/sample_network_topology/migrations/0002_json_properties.py
new file mode 100644
index 00000000..5802ed0b
--- /dev/null
+++ b/tests/openwisp2/sample_network_topology/migrations/0002_json_properties.py
@@ -0,0 +1,47 @@
+# Generated by Django 3.0.7 on 2020-06-25 18:25
+
+import collections
+from django.db import migrations
+import jsonfield.fields
+import rest_framework.utils.encoders
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('sample_network_topology', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='link',
+            name='properties',
+            field=jsonfield.fields.JSONField(
+                blank=True,
+                default=dict,
+                dump_kwargs={
+                    'cls': rest_framework.utils.encoders.JSONEncoder,
+                    'indent': 4,
+                },
+                load_kwargs={'object_pairs_hook': collections.OrderedDict},
+            ),
+        ),
+        migrations.AlterField(
+            model_name='node',
+            name='addresses',
+            field=jsonfield.fields.JSONField(blank=True, default=[]),
+        ),
+        migrations.AlterField(
+            model_name='node',
+            name='properties',
+            field=jsonfield.fields.JSONField(
+                blank=True,
+                default=dict,
+                dump_kwargs={
+                    'cls': rest_framework.utils.encoders.JSONEncoder,
+                    'indent': 4,
+                },
+                load_kwargs={'object_pairs_hook': collections.OrderedDict},
+            ),
+        ),
+    ]