diff --git a/sql/mysql-compatibility.md b/sql/mysql-compatibility.md
index 606498445185f..f878307912329 100644
--- a/sql/mysql-compatibility.md
+++ b/sql/mysql-compatibility.md
@@ -27,6 +27,7 @@ However, in TiDB, the following MySQL features are not supported for the time be
 + Drop primary key
 + SYS schema
 + Optimizer trace
++ X-Protocol
 
 ## Features that are different from MySQL