diff --git a/apps/emqx_s3/src/emqx_s3_client.erl b/apps/emqx_s3/src/emqx_s3_client.erl
index e3e1d84af..3bc5861c6 100644
--- a/apps/emqx_s3/src/emqx_s3_client.erl
+++ b/apps/emqx_s3/src/emqx_s3_client.erl
@@ -57,7 +57,7 @@
     port := part_number(),
     bucket := string(),
     headers := headers(),
-    acl := emqx_s3:acl(),
+    acl := emqx_s3:acl() | undefined,
     url_expire_time := pos_integer(),
     access_key_id := string() | undefined,
     secret_access_key := string() | undefined,
diff --git a/apps/emqx_s3/src/emqx_s3_schema.erl b/apps/emqx_s3/src/emqx_s3_schema.erl
index 23e69ec5d..5866f8c2b 100644
--- a/apps/emqx_s3/src/emqx_s3_schema.erl
+++ b/apps/emqx_s3/src/emqx_s3_schema.erl
@@ -105,7 +105,6 @@ fields(s3) ->
                     bucket_owner_full_control
                 ]),
                 #{
-                    default => private,
                     desc => ?DESC("acl"),
                     required => false
                 }
diff --git a/apps/emqx_s3/test/emqx_s3_schema_SUITE.erl b/apps/emqx_s3/test/emqx_s3_schema_SUITE.erl
index 89ec8a958..63f659da0 100644
--- a/apps/emqx_s3/test/emqx_s3_schema_SUITE.erl
+++ b/apps/emqx_s3/test/emqx_s3_schema_SUITE.erl
@@ -23,7 +23,6 @@ t_minimal_config(_Config) ->
             bucket := "bucket",
             host := "s3.us-east-1.endpoint.com",
             port := 443,
-            acl := private,
             min_part_size := 5242880,
             transport_options :=
                 #{