diff --git a/annuaire/settings/local.py b/annuaire/settings/local.py
index 7275ef6..22be900 100644
--- a/annuaire/settings/local.py
+++ b/annuaire/settings/local.py
@@ -57,6 +57,6 @@ def show_toolbar(request):
 
 
 if not TESTING:
-    INSTALLED_APPS += ["debug_toolbar"]
+    INSTALLED_APPS = INSTALLED_APPS + ["debug_toolbar"]
     MIDDLEWARE = ["debug_toolbar.middleware.DebugToolbarMiddleware"] + MIDDLEWARE
     DEBUG_TOOLBAR_CONFIG = {"SHOW_TOOLBAR_CALLBACK": show_toolbar}