diff --git a/ptcoffee/settings.py b/ptcoffee/settings.py
index f38cd99..784ca5d 100644
--- a/ptcoffee/settings.py
+++ b/ptcoffee/settings.py
@@ -103,8 +103,8 @@ MIDDLEWARE = [
 ]
 
 if DEBUG:
-    INSTALLED_APPS + ['debug_toolbar']
-    MIDDLEWARE + ['debug_toolbar.middleware.DebugToolbarMiddleware']
+    INSTALLED_APPS += ['debug_toolbar']
+    MIDDLEWARE += ['debug_toolbar.middleware.DebugToolbarMiddleware']
 
 
 ROOT_URLCONF = 'ptcoffee.urls'