diff --git a/etc/nanomq.conf b/etc/nanomq.conf
index 54818336..f06813c1 100644
--- a/etc/nanomq.conf
+++ b/etc/nanomq.conf
@@ -6,7 +6,7 @@
 
 mqtt {
     property_size = 32
-    max_packet_size = 260MB
+    max_packet_size = 256MB
     max_mqueue_len = 2048
     retry_interval = 10s
     keepalive_multiplier = 1.25