diff --git a/tests/openwisp2/settings.py b/tests/openwisp2/settings.py
index 0b8635db..75d12521 100644
--- a/tests/openwisp2/settings.py
+++ b/tests/openwisp2/settings.py
@@ -223,7 +223,7 @@
 if os.environ.get('SAMPLE_APP', False):
     INSTALLED_APPS.remove('openwisp_network_topology')
     INSTALLED_APPS.remove('openwisp_network_topology.integrations.device')
-    EXTENDED_APPS = ['openwisp_network_topology']
+    EXTENDED_APPS.append('openwisp_network_topology')
     INSTALLED_APPS += [
         'openwisp2.sample_network_topology',
         'openwisp2.sample_integration_device',