diff --git a/executor/set_test.go b/executor/set_test.go
index 015292f5d8308..35c61825ac494 100644
--- a/executor/set_test.go
+++ b/executor/set_test.go
@@ -141,37 +141,48 @@ func (s *testSuite) TestSetVar(c *C) {
 	tk.MustExec("SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED")
 	tk.MustQuery("select @@session.tx_isolation").Check(testkit.Rows("READ-COMMITTED"))
 	tk.MustQuery("select @@session.transaction_isolation").Check(testkit.Rows("READ-COMMITTED"))
-	tk.MustExec("SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED")
-	tk.MustQuery("select @@session.tx_isolation").Check(testkit.Rows("READ-UNCOMMITTED"))
-	tk.MustQuery("select @@session.transaction_isolation").Check(testkit.Rows("READ-UNCOMMITTED"))
-	tk.MustExec("SET GLOBAL TRANSACTION ISOLATION LEVEL SERIALIZABLE")
-	tk.MustQuery("select @@global.tx_isolation").Check(testkit.Rows("SERIALIZABLE"))
-	tk.MustQuery("select @@global.transaction_isolation").Check(testkit.Rows("SERIALIZABLE"))
+	// error
+	_, err = tk.Exec("SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED")
+	c.Assert(terror.ErrorEqual(err, variable.ErrUnsupportedValueForVar), IsTrue, Commentf("err %v", err))
+	tk.MustQuery("select @@session.tx_isolation").Check(testkit.Rows("READ-COMMITTED"))
+	tk.MustQuery("select @@session.transaction_isolation").Check(testkit.Rows("READ-COMMITTED"))
+	// Fails
+	_, err = tk.Exec("SET GLOBAL TRANSACTION ISOLATION LEVEL SERIALIZABLE")
+	c.Assert(terror.ErrorEqual(err, variable.ErrUnsupportedValueForVar), IsTrue, Commentf("err %v", err))
+	tk.MustQuery("select @@global.tx_isolation").Check(testkit.Rows("REPEATABLE-READ"))
+	tk.MustQuery("select @@global.transaction_isolation").Check(testkit.Rows("REPEATABLE-READ"))
 
 	// test synonyms variables
 	tk.MustExec("SET SESSION tx_isolation = 'READ-COMMITTED'")
 	tk.MustQuery("select @@session.tx_isolation").Check(testkit.Rows("READ-COMMITTED"))
 	tk.MustQuery("select @@session.transaction_isolation").Check(testkit.Rows("READ-COMMITTED"))
 
-	tk.MustExec("SET SESSION tx_isolation = 'READ-UNCOMMITTED'")
-	tk.MustQuery("select @@session.tx_isolation").Check(testkit.Rows("READ-UNCOMMITTED"))
-	tk.MustQuery("select @@session.transaction_isolation").Check(testkit.Rows("READ-UNCOMMITTED"))
+	_, err = tk.Exec("SET SESSION tx_isolation = 'READ-UNCOMMITTED'")
+	c.Assert(terror.ErrorEqual(err, variable.ErrUnsupportedValueForVar), IsTrue, Commentf("err %v", err))
+	tk.MustQuery("select @@session.tx_isolation").Check(testkit.Rows("READ-COMMITTED"))
+	tk.MustQuery("select @@session.transaction_isolation").Check(testkit.Rows("READ-COMMITTED"))
 
-	tk.MustExec("SET SESSION transaction_isolation = 'SERIALIZABLE'")
-	tk.MustQuery("select @@session.tx_isolation").Check(testkit.Rows("SERIALIZABLE"))
-	tk.MustQuery("select @@session.transaction_isolation").Check(testkit.Rows("SERIALIZABLE"))
+	// fails
+	_, err = tk.Exec("SET SESSION transaction_isolation = 'SERIALIZABLE'")
+	c.Assert(terror.ErrorEqual(err, variable.ErrUnsupportedValueForVar), IsTrue, Commentf("err %v", err))
+	tk.MustQuery("select @@session.tx_isolation").Check(testkit.Rows("READ-COMMITTED"))
+	tk.MustQuery("select @@session.transaction_isolation").Check(testkit.Rows("READ-COMMITTED"))
 
-	tk.MustExec("SET GLOBAL transaction_isolation = 'SERIALIZABLE'")
-	tk.MustQuery("select @@global.tx_isolation").Check(testkit.Rows("SERIALIZABLE"))
-	tk.MustQuery("select @@global.transaction_isolation").Check(testkit.Rows("SERIALIZABLE"))
+	// fails
+	_, err = tk.Exec("SET GLOBAL transaction_isolation = 'SERIALIZABLE'")
+	c.Assert(terror.ErrorEqual(err, variable.ErrUnsupportedValueForVar), IsTrue, Commentf("err %v", err))
+	tk.MustQuery("select @@global.tx_isolation").Check(testkit.Rows("REPEATABLE-READ"))
+	tk.MustQuery("select @@global.transaction_isolation").Check(testkit.Rows("REPEATABLE-READ"))
 
-	tk.MustExec("SET GLOBAL transaction_isolation = 'READ-UNCOMMITTED'")
-	tk.MustQuery("select @@global.tx_isolation").Check(testkit.Rows("READ-UNCOMMITTED"))
-	tk.MustQuery("select @@global.transaction_isolation").Check(testkit.Rows("READ-UNCOMMITTED"))
+	_, err = tk.Exec("SET GLOBAL transaction_isolation = 'READ-UNCOMMITTED'")
+	c.Assert(terror.ErrorEqual(err, variable.ErrUnsupportedValueForVar), IsTrue, Commentf("err %v", err))
+	tk.MustQuery("select @@global.tx_isolation").Check(testkit.Rows("REPEATABLE-READ"))
+	tk.MustQuery("select @@global.transaction_isolation").Check(testkit.Rows("REPEATABLE-READ"))
 
-	tk.MustExec("SET GLOBAL tx_isolation = 'SERIALIZABLE'")
-	tk.MustQuery("select @@global.tx_isolation").Check(testkit.Rows("SERIALIZABLE"))
-	tk.MustQuery("select @@global.transaction_isolation").Check(testkit.Rows("SERIALIZABLE"))
+	_, err = tk.Exec("SET GLOBAL tx_isolation = 'SERIALIZABLE'")
+	c.Assert(terror.ErrorEqual(err, variable.ErrUnsupportedValueForVar), IsTrue, Commentf("err %v", err))
+	tk.MustQuery("select @@global.tx_isolation").Check(testkit.Rows("REPEATABLE-READ"))
+	tk.MustQuery("select @@global.transaction_isolation").Check(testkit.Rows("REPEATABLE-READ"))
 
 	tk.MustExec("SET SESSION tx_read_only = 1")
 	tk.MustExec("SET SESSION tx_read_only = 0")
@@ -553,7 +564,6 @@ func (s *testSuite) TestValidateSetVar(c *C) {
 	result = tk.MustQuery("select @@tx_isolation;")
 	result.Check(testkit.Rows("REPEATABLE-READ"))
 
-	tk.MustExec("set @@tx_isolation='SERIALIZABLE'")
-	result = tk.MustQuery("select @@tx_isolation;")
-	result.Check(testkit.Rows("SERIALIZABLE"))
+	_, err = tk.Exec("set @@tx_isolation='SERIALIZABLE'")
+	c.Assert(terror.ErrorEqual(err, variable.ErrUnsupportedValueForVar), IsTrue, Commentf("err %v", err))
 }
diff --git a/sessionctx/variable/session.go b/sessionctx/variable/session.go
index 384c588698057..bc1ea077ebc68 100644
--- a/sessionctx/variable/session.go
+++ b/sessionctx/variable/session.go
@@ -582,6 +582,10 @@ func (s *SessionVars) WithdrawAllPreparedStmt() {
 func (s *SessionVars) SetSystemVar(name string, val string) error {
 	switch name {
 	case TxnIsolationOneShot:
+		switch val {
+		case "SERIALIZABLE", "READ-UNCOMMITTED":
+			return ErrUnsupportedValueForVar.GenWithStackByArgs(name, val)
+		}
 		s.TxnIsolationLevelOneShot.State = 1
 		s.TxnIsolationLevelOneShot.Value = val
 	case TimeZone:
diff --git a/sessionctx/variable/varsutil.go b/sessionctx/variable/varsutil.go
index 4d55292c61ff3..c5f3aa3c1e1d9 100644
--- a/sessionctx/variable/varsutil.go
+++ b/sessionctx/variable/varsutil.go
@@ -394,6 +394,10 @@ func ValidateSetSystemVar(vars *SessionVars, name string, value string) (string,
 		if !exists {
 			return "", ErrWrongValueForVar.GenWithStackByArgs(name, value)
 		}
+		switch upVal {
+		case "SERIALIZABLE", "READ-UNCOMMITTED":
+			return "", ErrUnsupportedValueForVar.GenWithStackByArgs(name, value)
+		}
 		return upVal, nil
 	}
 	return value, nil