diff --git a/session/bootstrap.go b/session/bootstrap.go
index 5039f813de304..a00c5159232bc 100644
--- a/session/bootstrap.go
+++ b/session/bootstrap.go
@@ -95,8 +95,8 @@ const (
 	// CreateTablePrivTable is the SQL statement creates table scope privilege table in system db.
 	CreateTablePrivTable = `CREATE TABLE if not exists mysql.tables_priv (
 		Host		CHAR(60),
-		DB			CHAR(64),
-		User		CHAR(16),
+		DB		CHAR(64),
+		User		CHAR(32),
 		Table_name	CHAR(64),
 		Grantor		CHAR(77),
 		Timestamp	Timestamp DEFAULT CURRENT_TIMESTAMP,
@@ -106,8 +106,8 @@ const (
 	// CreateColumnPrivTable is the SQL statement creates column scope privilege table in system db.
 	CreateColumnPrivTable = `CREATE TABLE if not exists mysql.columns_priv(
 		Host		CHAR(60),
-		DB			CHAR(64),
-		User		CHAR(16),
+		DB		CHAR(64),
+		User		CHAR(32),
 		Table_name	CHAR(64),
 		Column_name	CHAR(64),
 		Timestamp	Timestamp DEFAULT CURRENT_TIMESTAMP,
@@ -585,6 +585,8 @@ func upgradeToVer18(s Session) {
 
 func upgradeToVer19(s Session) {
 	doReentrantDDL(s, "ALTER TABLE mysql.db MODIFY User CHAR(32)")
+	doReentrantDDL(s, "ALTER TABLE mysql.tables_priv MODIFY User CHAR(32)")
+	doReentrantDDL(s, "ALTER TABLE mysql.columns_priv MODIFY User CHAR(32)")
 }
 
 // updateBootstrapVer updates bootstrap version variable in mysql.TiDB table.
diff --git a/session/session_test.go b/session/session_test.go
index 424df255b4c2e..fb5b75d8a154e 100644
--- a/session/session_test.go
+++ b/session/session_test.go
@@ -1978,6 +1978,8 @@ func (s *testSessionSuite) TestRollbackOnCompileError(c *C) {
 
 func (s *testSessionSuite) TestDBUserNameLength(c *C) {
 	tk := testkit.NewTestKitWithInit(c, s.store)
+	tk.MustExec("create table if not exists t (a int)")
 	// Test user name lengh can be longer than 16.
 	tk.MustExec(`grant all privileges on test.* to 'abcddfjakldfjaldddds'@'%' identified by ''`)
+	tk.MustExec(`grant all privileges on test.t to 'abcddfjakldfjaldddds'@'%' identified by ''`)
 }