diff --git a/ext/mysqlnd/mysqlnd_enum_n_def.h b/ext/mysqlnd/mysqlnd_enum_n_def.h
index 1d645a8d75c..4ace69adcf9 100644
--- a/ext/mysqlnd/mysqlnd_enum_n_def.h
+++ b/ext/mysqlnd/mysqlnd_enum_n_def.h
@@ -43,7 +43,7 @@
 #define MYSQLND_SQLSTATE_LENGTH		5
 #define MYSQLND_SQLSTATE_NULL		"00000"
 
-#define MYSQLND_MAX_ALLOWED_USER_LEN	256		/* 64 char * 4byte . MySQL supports now only 16 char, but let it be forward compatible */
+#define MYSQLND_MAX_ALLOWED_USER_LEN	252		/* 63 char * 4byte . MySQL supports now only 16 char, but let it be forward compatible */
 #define MYSQLND_MAX_ALLOWED_DB_LEN		1024	/* 256 char * 4byte. MySQL supports now only 64 char in the tables, but on the FS could be different. Forward compatible. */
 
 #define MYSQLND_NET_CMD_BUFFER_MIN_SIZE			4096