diff --git a/django/db/utils.py b/django/db/utils.py
index 8dbfc117a598a..a1a2c0b564940 100644
--- a/django/db/utils.py
+++ b/django/db/utils.py
@@ -173,7 +173,7 @@ def ensure_defaults(self, alias):
             conn.setdefault('AUTOCOMMIT', False)
         conn.setdefault('AUTOCOMMIT', True)
         conn.setdefault('ENGINE', 'django.db.backends.dummy')
-        if conn['ENGINE'] == 'django.db.backends.':
+        if conn['ENGINE'] == 'django.db.backends.' or not conn['ENGINE']:
             conn['ENGINE'] = 'django.db.backends.dummy'
         conn.setdefault('CONN_MAX_AGE', 0)
         conn.setdefault('OPTIONS', {})