diff --git a/apps/emqx/etc/emqx.conf b/apps/emqx/etc/emqx.conf
index 372ea99b7..b5c2c1f73 100644
--- a/apps/emqx/etc/emqx.conf
+++ b/apps/emqx/etc/emqx.conf
@@ -1,4 +1,3 @@
-
 listeners.tcp.default {
   bind: "0.0.0.0:1883"
   max_connections: 1024000
diff --git a/apps/emqx/src/emqx_schema.erl b/apps/emqx/src/emqx_schema.erl
index 8f836a3dc..379492588 100644
--- a/apps/emqx/src/emqx_schema.erl
+++ b/apps/emqx/src/emqx_schema.erl
@@ -1017,7 +1017,10 @@ fields("tcp_opts") ->
         {"buffer",
             sc(
                 bytesize(),
-                #{desc => ?DESC(fields_tcp_opts_buffer)}
+                #{
+                    desc => ?DESC(fields_tcp_opts_buffer),
+                    default => "4KB"
+                }
             )},
         {"high_watermark",
             sc(