diff --git a/mongoengine/connection.py b/mongoengine/connection.py
index 2ea572df..cde3ccd4 100644
--- a/mongoengine/connection.py
+++ b/mongoengine/connection.py
@@ -141,6 +141,7 @@ def get_connection(alias=DEFAULT_CONNECTION_NAME, reconnect=False):
                 connection_settings.pop('name', None)
                 connection_settings.pop('username', None)
                 connection_settings.pop('password', None)
+                connection_settings.pop('authentication_source', None)
                 if conn_settings == connection_settings and _connections.get(db_alias, None):
                     connection = _connections[db_alias]
                     break