diff --git a/executor/executor_write_test.go b/executor/executor_write_test.go
index 094a7c7122..996bf0989d 100644
--- a/executor/executor_write_test.go
+++ b/executor/executor_write_test.go
@@ -102,6 +102,10 @@ func (s *testSuite) TestInsert(c *C) {
 
 	_, err = tk.Exec(`insert into insert_test (id, c2) values(1, 1) on duplicate key update t.c2 = 10`)
 	c.Assert(err, NotNil)
+
+	tk.MustExec("create table insert_err (id int, c1 varchar(8))")
+	_, err = tk.Exec("insert insert_err values (1, 'abcdabcdabcd')")
+	c.Assert(types.ErrDataTooLong.Equal(err), IsTrue)
 }
 
 func (s *testSuite) TestInsertAutoInc(c *C) {
diff --git a/terror/terror.go b/terror/terror.go
index aa80fdfa65..24ef348191 100644
--- a/terror/terror.go
+++ b/terror/terror.go
@@ -75,6 +75,7 @@ const (
 	ClassVariable
 	ClassXEval
 	ClassTable
+	ClassTypes
 	// Add more as needed.
 )
 
@@ -115,6 +116,8 @@ func (ec ErrClass) String() string {
 		return "variable"
 	case ClassTable:
 		return "table"
+	case ClassTypes:
+		return "types"
 	}
 	return strconv.Itoa(int(ec))
 }
diff --git a/util/types/convert_test.go b/util/types/convert_test.go
index dbe4879ce1..25559a3999 100644
--- a/util/types/convert_test.go
+++ b/util/types/convert_test.go
@@ -39,13 +39,13 @@ func (s *testTypeConvertSuite) TestConvertType(c *C) {
 	ft.Flen = 4
 	ft.Charset = "utf8"
 	v, err := Convert("123456", ft)
-	c.Assert(err, IsNil)
+	c.Assert(ErrDataTooLong.Equal(err), IsTrue)
 	c.Assert(v, Equals, "1234")
 	ft = NewFieldType(mysql.TypeString)
 	ft.Flen = 4
 	ft.Charset = charset.CharsetBin
 	v, err = Convert("12345", ft)
-	c.Assert(err, IsNil)
+	c.Assert(ErrDataTooLong.Equal(err), IsTrue)
 	c.Assert(v, DeepEquals, []byte("1234"))
 
 	ft = NewFieldType(mysql.TypeFloat)
@@ -120,13 +120,13 @@ func (s *testTypeConvertSuite) TestConvertType(c *C) {
 	ft = NewFieldType(mysql.TypeString)
 	ft.Flen = 3
 	v, err = Convert("12345", ft)
-	c.Assert(err, IsNil)
+	c.Assert(ErrDataTooLong.Equal(err), IsTrue)
 	c.Assert(v, Equals, "123")
 	ft = NewFieldType(mysql.TypeString)
 	ft.Flen = 3
 	ft.Charset = charset.CharsetBin
 	v, err = Convert("12345", ft)
-	c.Assert(err, IsNil)
+	c.Assert(ErrDataTooLong.Equal(err), IsTrue)
 	c.Assert(v, DeepEquals, []byte("123"))
 
 	// For TypeDuration
diff --git a/util/types/datum.go b/util/types/datum.go
index f4633dc43a..eaeee6aa2b 100644
--- a/util/types/datum.go
+++ b/util/types/datum.go
@@ -762,12 +762,16 @@ func (d *Datum) convertToString(target *FieldType) (Datum, error) {
 		return invalidConv(d, target.Tp)
 	}
 	// TODO: consider target.Charset/Collate
+	var err error
+	if target.Flen > 0 && target.Flen < len(s) {
+		err = ErrDataTooLong.Gen("Data Too Long, field len %d, data len %d", target.Flen, len(s))
+	}
 	s = truncateStr(s, target.Flen)
 	ret.SetString(s)
 	if target.Charset == charset.CharsetBin {
 		ret.k = KindBytes
 	}
-	return ret, nil
+	return ret, errors.Trace(err)
 }
 
 func (d *Datum) convertToInt(target *FieldType) (Datum, error) {
diff --git a/util/types/errors.go b/util/types/errors.go
new file mode 100644
index 0000000000..9d97ae08c5
--- /dev/null
+++ b/util/types/errors.go
@@ -0,0 +1,35 @@
+// Copyright 2016 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package types
+
+import (
+	"github.com/pingcap/tidb/mysql"
+	"github.com/pingcap/tidb/terror"
+)
+
+var (
+	// ErrDataTooLong is returned when converts a string value that is longer than field type length.
+	ErrDataTooLong *terror.Error = terror.ClassTypes.New(codeDataTooLong, "Data Too Long")
+)
+
+const (
+	codeDataTooLong terror.ErrCode = terror.ErrCode(mysql.ErrDataTooLong)
+)
+
+func init() {
+	typesMySQLErrCodes := map[terror.ErrCode]uint16{
+		codeDataTooLong: mysql.ErrDataTooLong,
+	}
+	terror.ErrClassToMySQLCodes[terror.ClassTypes] = typesMySQLErrCodes
+}