diff --git a/docs/contributing/developing.rst b/docs/contributing/developing.rst
index a2e41d4d1a..3ac0a68349 100644
--- a/docs/contributing/developing.rst
+++ b/docs/contributing/developing.rst
@@ -71,17 +71,23 @@ an argument to ``runtests.py``::
 
 **Testing against PostgreSQL**
 
-By default, Wagtail tests against SQLite. If you need to test against a
-different database, set the ``DATABASE_ENGINE`` environment variable to the
-name of the Django database backend to test against::
+By default, Wagtail tests against SQLite. You can switch to using PostgreSQL by
+using the ``--postgres`` argument::
 
-    DATABASE_ENGINE=django.db.backends.postgresql_psycopg2 python runtests.py
-
-This will create a new database called ``test_wagtail`` in PostgreSQL and run
-the tests against it.
+    python runtests.py --postgres
 
 If you need to use a different user, password or host. Use the ``PGUSER``, ``PGPASSWORD`` and ``PGHOST`` environment variables.
 
+**Testing against a different database**
+
+If you need to test against a different database, set the ``DATABASE_ENGINE``
+environment variable to the name of the Django database backend to test against::
+
+    DATABASE_ENGINE=django.db.backends.mysql python runtests.py
+
+This will create a new database called ``test_wagtail`` in MySQL and run
+the tests against it.
+
 **Testing Elasticsearch**
 
 To test Elasticsearch, you need to have the ``elasticsearch`` package installed.
diff --git a/runtests.py b/runtests.py
index a1925f907d..1a674c29a1 100755
--- a/runtests.py
+++ b/runtests.py
@@ -1,4 +1,5 @@
 #!/usr/bin/env python
+
 import sys
 import os
 import shutil
@@ -6,8 +7,6 @@ import warnings
 
 from django.core.management import execute_from_command_line
 
-from wagtail.tests.settings import STATIC_ROOT, MEDIA_ROOT
-
 
 os.environ['DJANGO_SETTINGS_MODULE'] = 'wagtail.tests.settings'
 
@@ -17,10 +16,17 @@ def runtests():
     warnings.simplefilter('default', DeprecationWarning)
     warnings.simplefilter('default', PendingDeprecationWarning)
 
-    argv = sys.argv[:1] + ['test'] + sys.argv[1:]
+    args = sys.argv[1:]
+
+    if '--postgres' in args:
+        os.environ['DATABASE_ENGINE'] = 'django.db.backends.postgresql_psycopg2'
+        args.remove('--postgres')
+
+    argv = sys.argv[:1] + ['test'] + args
     try:
         execute_from_command_line(argv)
     finally:
+        from wagtail.tests.settings import STATIC_ROOT, MEDIA_ROOT
         shutil.rmtree(STATIC_ROOT, ignore_errors=True)
         shutil.rmtree(MEDIA_ROOT, ignore_errors=True)