diff --git a/CHANGES-4.3.md b/CHANGES-4.3.md
index e14b7371e..38f4cbb48 100644
--- a/CHANGES-4.3.md
+++ b/CHANGES-4.3.md
@@ -15,7 +15,9 @@ File format:
 
 - TLS listener memory usage optimization
   new option 'hibernate_after' to hibernate TLS process after idling
-
+- TLS listener default buffer size to 4KB
+  Eliminate uncertainty that the buffer size is set by OS default
+  
 ## v4.3.20
 
 ### Bug fixes
diff --git a/etc/emqx.conf b/etc/emqx.conf
index 19f85a877..7b1bf1ef0 100644
--- a/etc/emqx.conf
+++ b/etc/emqx.conf
@@ -1609,14 +1609,14 @@ listener.ssl.external.ciphers = TLS_AES_256_GCM_SHA384,TLS_AES_128_GCM_SHA256,TL
 ## See: listener.tcp.$name.recbuf
 ##
 ## Value: Bytes
-## listener.ssl.external.recbuf = 4KB
+listener.ssl.external.recbuf = 4KB
 
 ## The TCP send buffer(os kernel) for internal MQTT connections.
 ##
 ## See: listener.tcp.$name.sndbuf
 ##
 ## Value: Bytes
-## listener.ssl.external.sndbuf = 4KB
+listener.ssl.external.sndbuf = 4KB
 
 ## The size of the user-level software buffer used by the driver.
 ##