diff --git a/docs/ref/contrib/gis/testing.txt b/docs/ref/contrib/gis/testing.txt
index d601b413e9..4ef58f3934 100644
--- a/docs/ref/contrib/gis/testing.txt
+++ b/docs/ref/contrib/gis/testing.txt
@@ -169,6 +169,8 @@ in :mod:`django.contrib.gis`::
        }
     }
 
+    SECRET_KEY = 'django_tests_secret_key'
+
 Assuming the settings above were in a ``postgis.py`` file in the same
 directory as ``runtests.py``, then all Django and GeoDjango tests would
 be performed when executing the command::