diff --git a/openwisp_monitoring/device/apps.py b/openwisp_monitoring/device/apps.py
index 74b78c213..fb6685ff6 100644
--- a/openwisp_monitoring/device/apps.py
+++ b/openwisp_monitoring/device/apps.py
@@ -3,7 +3,7 @@
 from django.apps import AppConfig
 from django.conf import settings
 from django.core.cache import cache
-from django.db.models import Case, Count, Sum, When
+from django.db.models import Count
 from django.db.models.signals import post_delete, post_save
 from django.urls import reverse_lazy
 from django.utils.translation import gettext_lazy as _
@@ -350,30 +350,21 @@ def register_dashboard_items(self):
                     'query_params': {
                         'app_label': WifiSession._meta.app_label,
                         'model': WifiSession._meta.model_name,
-                        'annotate': {
-                            'active': Count(
-                                Case(
-                                    When(
-                                        stop_time__isnull=True,
-                                        then=1,
-                                    )
-                                )
-                            ),
-                        },
+                        'filter': {'stop_time__isnull': True},
                         'aggregate': {
-                            'active__sum': Sum('active'),
+                            'active__count': Count('id'),
                         },
                         'organization_field': 'device__organization_id',
                     },
                     'filters': {
                         'key': 'stop_time__isnull',
-                        'active__sum': 'true',
+                        'active__count': 'true',
                     },
                     'colors': {
-                        'active__sum': '#267126',
+                        'active__count': '#267126',
                     },
                     'labels': {
-                        'active__sum': _('Currently Active WiFi Sessions'),
+                        'active__count': _('Currently Active WiFi Sessions'),
                     },
                     'quick_link': {
                         'url': reverse_lazy(
diff --git a/openwisp_monitoring/device/tests/test_admin.py b/openwisp_monitoring/device/tests/test_admin.py
index c156ccc96..679685412 100644
--- a/openwisp_monitoring/device/tests/test_admin.py
+++ b/openwisp_monitoring/device/tests/test_admin.py
@@ -5,6 +5,7 @@
 from django.contrib.auth.models import Permission
 from django.contrib.contenttypes.forms import generic_inlineformset_factory
 from django.core.cache import cache
+from django.db import connection
 from django.test import TestCase
 from django.urls import reverse
 from django.utils.timezone import datetime, now, timedelta
@@ -118,6 +119,22 @@ def test_dashboard_map_on_index(self):
         self.assertContains(response, "geoJsonUrl: \'http://testserver/api")
         self.assertContains(response, "locationDeviceUrl: \'http://testserver/api")
 
+    def test_wifisession_dashboard_chart_query(self):
+        url = reverse('admin:index')
+        with self.assertNumQueries(10):
+            response = self.client.get(url)
+        self.assertEqual(response.status_code, 200)
+        device_monitoring_app_label = WifiSession._meta.app_label
+        for query in connection.queries:
+            if query['sql'] == (
+                f'SELECT COUNT("{device_monitoring_app_label}_wifisession"."id") '
+                f'AS "active__count" FROM "{device_monitoring_app_label}_wifisession" '
+                f'WHERE "{device_monitoring_app_label}_wifisession"."stop_time" IS NULL'
+            ):
+                break
+        else:
+            self.fail('WiFiSession dashboard query not found')
+
     def test_status_data(self):
         d = self._create_device(organization=self._create_org())
         data = self._data()