diff --git a/scripts/tests_extension_hook.py b/scripts/tests_extension_hook.py
index dc97c24..f69d034 100644
--- a/scripts/tests_extension_hook.py
+++ b/scripts/tests_extension_hook.py
@@ -18,9 +18,13 @@ def django_plugin_hook(test_item: YamlTestItem) -> None:
     if 'SECRET_KEY' not in custom_settings:
         custom_settings = 'SECRET_KEY = "1"\n' + custom_settings
 
+    django_settings_section = "\n[mypy.plugins.django-stubs]\n" \
+                              "django_settings_module = mysettings"
     if not test_item.additional_mypy_config:
-        test_item.additional_mypy_config = "[mypy.plugins.django-stubs]\n" \
-                                           "django_settings_module = mysettings"
+        test_item.additional_mypy_config = django_settings_section
+    else:
+        if '[mypy.plugins.django-stubs]' not in test_item.additional_mypy_config:
+            test_item.additional_mypy_config += django_settings_section
 
     mysettings_file = File(path='mysettings.py', content=custom_settings)
     test_item.files.append(mysettings_file)