diff --git a/openwisp_monitoring/device/tests/__init__.py b/openwisp_monitoring/device/tests/__init__.py
index 98af8830..512a6ac4 100644
--- a/openwisp_monitoring/device/tests/__init__.py
+++ b/openwisp_monitoring/device/tests/__init__.py
@@ -86,10 +86,11 @@ def assertDataDict(self, dd_data, data):
         data = self._transform_wireless_interface_test_data(data)
         self.assertDictEqual(dd_data, data)
 
-    def create_test_data(self, no_resources=False):
+    def create_test_data(self, no_resources=False, data=None, assertions=True):
         o = self._create_org()
         d = self._create_device(organization=o)
-        data = self._data()
+        if not data:
+            data = self._data()
         # creation of resources metrics can be avoided in tests not involving them
         # this speeds up those tests by reducing requests made
         if no_resources:
@@ -97,6 +98,8 @@ def create_test_data(self, no_resources=False):
         r = self._post_data(d.id, d.key, data)
         self.assertEqual(r.status_code, 200)
         dd = DeviceData(pk=d.pk)
+        if not assertions:
+            return dd
         self.assertDataDict(dd.data, data)
         if no_resources:
             metric_count, chart_count = 4, 4
diff --git a/openwisp_monitoring/device/tests/test_api.py b/openwisp_monitoring/device/tests/test_api.py
index 4bcec5ef..03a7c621 100644
--- a/openwisp_monitoring/device/tests/test_api.py
+++ b/openwisp_monitoring/device/tests/test_api.py
@@ -1378,6 +1378,36 @@ def _assert_chart_group(url, status_code, expected):
             self.assertEqual(rows[-2].strip().split(','), ['ssh', '100.0'])
             self.assertEqual(rows[-1].strip().split(','), ['http2', '90.0'])
 
+    def test_missing_rx_bytes(self):
+        """
+        Regression test for:
+        https://github.com/openwisp/openwisp-monitoring/issues/595
+        """
+        data = self._data()
+        del data['interfaces'][0]['statistics']['rx_bytes']
+        dd = self.create_test_data(no_resources=True, data=data, assertions=False)
+        qs = Metric.objects.filter(
+            object_id=dd.pk, key='traffic', main_tags={'ifname': 'wlan0'}
+        )
+        self.assertEqual(qs.count(), 1)
+        m = qs.first()
+        points = self._read_metric(m, limit=1, extra_fields=['tx_bytes'])
+        self.assertEqual(points[0].get('tx_bytes'), 145)
+        self.assertEqual(points[0].get('rx_bytes'), 0)
+
+    def test_missing_tx_bytes(self):
+        data = self._data()
+        del data['interfaces'][0]['statistics']['tx_bytes']
+        dd = self.create_test_data(no_resources=True, data=data, assertions=False)
+        qs = Metric.objects.filter(
+            object_id=dd.pk, key='traffic', main_tags={'ifname': 'wlan0'}
+        )
+        self.assertEqual(qs.count(), 1)
+        m = qs.first()
+        points = self._read_metric(m, limit=1, extra_fields=['tx_bytes'])
+        self.assertEqual(points[0].get('rx_bytes'), 324)
+        self.assertEqual(points[0].get('tx_bytes'), 0)
+
 
 class TestGeoApi(TestGeoMixin, AuthenticationMixin, DeviceMonitoringTestCase):
     location_model = Location
diff --git a/openwisp_monitoring/device/writer.py b/openwisp_monitoring/device/writer.py
index f09e4824..0d7950dc 100644
--- a/openwisp_monitoring/device/writer.py
+++ b/openwisp_monitoring/device/writer.py
@@ -79,14 +79,14 @@ def write(self, data, time=None, current=False):
             # Explicitly stated None to avoid skipping in case the stats are zero
             if (
                 ifstats.get('rx_bytes') is not None
-                and ifstats.get('rx_bytes') is not None
+                or ifstats.get('tx_bytes') is not None
             ):
                 field_value = self._calculate_increment(
-                    ifname, 'rx_bytes', ifstats['rx_bytes']
+                    ifname, 'rx_bytes', ifstats.get('rx_bytes', 0)
                 )
                 extra_values = {
                     'tx_bytes': self._calculate_increment(
-                        ifname, 'tx_bytes', ifstats['tx_bytes']
+                        ifname, 'tx_bytes', ifstats.get('tx_bytes', 0)
                     )
                 }
                 name = f'{ifname} traffic'