diff --git a/apps/emqx_auth_mongo/etc/emqx_auth_mongo.conf b/apps/emqx_auth_mongo/etc/emqx_auth_mongo.conf
index 3d3d0ee5b..8baddae19 100644
--- a/apps/emqx_auth_mongo/etc/emqx_auth_mongo.conf
+++ b/apps/emqx_auth_mongo/etc/emqx_auth_mongo.conf
@@ -5,7 +5,7 @@
 ## MongoDB Topology Type.
 ##
 ## Value: single | unknown | sharded | rs
-auth.mongo.type = 
+auth.mongo.type = single
 
 ## Whether to use SRV and TXT records.
 ##