diff --git a/sys_conn_helper_linux.go b/sys_conn_helper_linux.go
index 622f4e6f..310c8374 100644
--- a/sys_conn_helper_linux.go
+++ b/sys_conn_helper_linux.go
@@ -19,7 +19,7 @@ const (
 	ipv4PKTINFO  = unix.IP_PKTINFO
 )
 
-const ecnIPv4DataLen = 4
+const ecnIPv4DataLen = 1
 
 const batchSize = 8 // needs to smaller than MaxUint8 (otherwise the type of oobConn.readPos has to be changed)