diff --git a/br/pkg/lightning/backend/local/engine.go b/br/pkg/lightning/backend/local/engine.go
index 32d004654233f..9bab661ab3e86 100644
--- a/br/pkg/lightning/backend/local/engine.go
+++ b/br/pkg/lightning/backend/local/engine.go
@@ -123,6 +123,8 @@ type Engine struct {
 	config    backend.LocalEngineConfig
 	tableInfo *checkpoints.TidbTableInfo
 
+	dupDetectOpt dupDetectOpt
+
 	// total size of SST files waiting to be ingested
 	pendingFileSize atomic.Int64
 
@@ -981,7 +983,7 @@ func (e *Engine) newKVIter(ctx context.Context, opts *pebble.IterOptions) Iter {
 		zap.String("table", common.UniqueTable(e.tableInfo.DB, e.tableInfo.Name)),
 		zap.Int64("tableID", e.tableInfo.ID),
 		zap.Stringer("engineUUID", e.UUID))
-	return newDupDetectIter(ctx, e.db, e.keyAdapter, opts, e.duplicateDB, logger)
+	return newDupDetectIter(ctx, e.db, e.keyAdapter, opts, e.duplicateDB, logger, e.dupDetectOpt)
 }
 
 type sstMeta struct {
diff --git a/br/pkg/lightning/backend/local/iterator.go b/br/pkg/lightning/backend/local/iterator.go
index e2cb3a447cfbb..29ed50b743773 100644
--- a/br/pkg/lightning/backend/local/iterator.go
+++ b/br/pkg/lightning/backend/local/iterator.go
@@ -21,6 +21,7 @@ import (
 
 	"github.com/cockroachdb/pebble"
 	sst "github.com/pingcap/kvproto/pkg/import_sstpb"
+	"github.com/pingcap/tidb/br/pkg/lightning/common"
 	"github.com/pingcap/tidb/br/pkg/lightning/log"
 	"github.com/pingcap/tidb/br/pkg/logutil"
 	"go.uber.org/multierr"
@@ -82,6 +83,11 @@ type dupDetectIter struct {
 	writeBatch     *pebble.Batch
 	writeBatchSize int64
 	logger         log.Logger
+	option         dupDetectOpt
+}
+
+type dupDetectOpt struct {
+	reportErrOnDup bool
 }
 
 func (d *dupDetectIter) Seek(key []byte) bool {
@@ -149,6 +155,14 @@ func (d *dupDetectIter) Next() bool {
 			d.curVal = append(d.curVal[:0], d.iter.Value()...)
 			return true
 		}
+		if d.option.reportErrOnDup {
+			dupKey := make([]byte, len(d.curKey))
+			dupVal := make([]byte, len(d.iter.Value()))
+			copy(dupKey, d.curKey)
+			copy(dupVal, d.curVal)
+			d.err = common.ErrFoundDuplicateKeys.FastGenByArgs(dupKey, dupVal)
+			return false
+		}
 		if !recordFirst {
 			d.record(d.curRawKey, d.curKey, d.curVal)
 			recordFirst = true
@@ -192,7 +206,7 @@ func (d *dupDetectIter) OpType() sst.Pair_OP {
 var _ Iter = &dupDetectIter{}
 
 func newDupDetectIter(ctx context.Context, db *pebble.DB, keyAdapter KeyAdapter,
-	opts *pebble.IterOptions, dupDB *pebble.DB, logger log.Logger) *dupDetectIter {
+	opts *pebble.IterOptions, dupDB *pebble.DB, logger log.Logger, dupOpt dupDetectOpt) *dupDetectIter {
 	newOpts := &pebble.IterOptions{TableFilter: opts.TableFilter}
 	if len(opts.LowerBound) > 0 {
 		newOpts.LowerBound = keyAdapter.Encode(nil, opts.LowerBound, math.MinInt64)
@@ -206,6 +220,7 @@ func newDupDetectIter(ctx context.Context, db *pebble.DB, keyAdapter KeyAdapter,
 		keyAdapter: keyAdapter,
 		writeBatch: dupDB.NewBatch(),
 		logger:     logger,
+		option:     dupOpt,
 	}
 }
 
diff --git a/br/pkg/lightning/backend/local/iterator_test.go b/br/pkg/lightning/backend/local/iterator_test.go
index 3abb6fbc3b06c..c183963443bae 100644
--- a/br/pkg/lightning/backend/local/iterator_test.go
+++ b/br/pkg/lightning/backend/local/iterator_test.go
@@ -122,7 +122,7 @@ func TestDupDetectIterator(t *testing.T) {
 	dupDB, err := pebble.Open(filepath.Join(storeDir, "duplicates"), &pebble.Options{})
 	require.NoError(t, err)
 	var iter Iter
-	iter = newDupDetectIter(context.Background(), db, keyAdapter, &pebble.IterOptions{}, dupDB, log.L())
+	iter = newDupDetectIter(context.Background(), db, keyAdapter, &pebble.IterOptions{}, dupDB, log.L(), dupDetectOpt{})
 	sort.Slice(pairs, func(i, j int) bool {
 		key1 := keyAdapter.Encode(nil, pairs[i].Key, pairs[i].RowID)
 		key2 := keyAdapter.Encode(nil, pairs[j].Key, pairs[j].RowID)
@@ -217,7 +217,7 @@ func TestDupDetectIterSeek(t *testing.T) {
 
 	dupDB, err := pebble.Open(filepath.Join(storeDir, "duplicates"), &pebble.Options{})
 	require.NoError(t, err)
-	iter := newDupDetectIter(context.Background(), db, keyAdapter, &pebble.IterOptions{}, dupDB, log.L())
+	iter := newDupDetectIter(context.Background(), db, keyAdapter, &pebble.IterOptions{}, dupDB, log.L(), dupDetectOpt{})
 
 	require.True(t, iter.Seek([]byte{1, 2, 3, 1}))
 	require.Equal(t, pairs[1].Val, iter.Value())
diff --git a/br/pkg/lightning/backend/local/local.go b/br/pkg/lightning/backend/local/local.go
index e32606207082e..73cd864927b01 100644
--- a/br/pkg/lightning/backend/local/local.go
+++ b/br/pkg/lightning/backend/local/local.go
@@ -369,6 +369,7 @@ type local struct {
 
 	checkTiKVAvaliable  bool
 	duplicateDetection  bool
+	duplicateDetectOpt  dupDetectOpt
 	duplicateDB         *pebble.DB
 	keyAdapter          KeyAdapter
 	errorMgr            *errormanager.ErrorManager
@@ -493,6 +494,7 @@ func NewLocalBackend(
 		engineMemCacheSize:      int(cfg.TikvImporter.EngineMemCacheSize),
 		localWriterMemCacheSize: int64(cfg.TikvImporter.LocalWriterMemCacheSize),
 		duplicateDetection:      duplicateDetection,
+		duplicateDetectOpt:      dupDetectOpt{duplicateDetection && cfg.TikvImporter.DuplicateResolution == config.DupeResAlgErr},
 		checkTiKVAvaliable:      cfg.App.CheckRequirements,
 		duplicateDB:             duplicateDB,
 		keyAdapter:              keyAdapter,
@@ -796,6 +798,7 @@ func (local *local) OpenEngine(ctx context.Context, cfg *backend.EngineConfig, e
 		config:             engineCfg,
 		tableInfo:          cfg.TableInfo,
 		duplicateDetection: local.duplicateDetection,
+		dupDetectOpt:       local.duplicateDetectOpt,
 		duplicateDB:        local.duplicateDB,
 		errorMgr:           local.errorMgr,
 		keyAdapter:         local.keyAdapter,
@@ -846,6 +849,7 @@ func (local *local) CloseEngine(ctx context.Context, cfg *backend.EngineConfig,
 			tableInfo:          cfg.TableInfo,
 			keyAdapter:         local.keyAdapter,
 			duplicateDetection: local.duplicateDetection,
+			dupDetectOpt:       local.duplicateDetectOpt,
 			duplicateDB:        local.duplicateDB,
 			errorMgr:           local.errorMgr,
 			logger:             log.FromContext(ctx),
diff --git a/br/pkg/lightning/common/errors.go b/br/pkg/lightning/common/errors.go
index 1b23ff99fc1b4..14645217636a4 100644
--- a/br/pkg/lightning/common/errors.go
+++ b/br/pkg/lightning/common/errors.go
@@ -97,6 +97,7 @@ var (
 	ErrInvalidMetaStatus    = errors.Normalize("invalid meta status: '%s'", errors.RFCCodeText("Lightning:Restore:ErrInvalidMetaStatus"))
 	ErrTableIsChecksuming   = errors.Normalize("table '%s' is checksuming", errors.RFCCodeText("Lightning:Restore:ErrTableIsChecksuming"))
 	ErrResolveDuplicateRows = errors.Normalize("resolve duplicate rows error on table '%s'", errors.RFCCodeText("Lightning:Restore:ErrResolveDuplicateRows"))
+	ErrFoundDuplicateKeys   = errors.Normalize("found duplicate key '%s', value '%s'", errors.RFCCodeText("Lightning:Restore:ErrFoundDuplicateKey"))
 )
 
 type withStack struct {
diff --git a/br/pkg/lightning/config/config.go b/br/pkg/lightning/config/config.go
index fdbe962433806..e1031c760f749 100644
--- a/br/pkg/lightning/config/config.go
+++ b/br/pkg/lightning/config/config.go
@@ -381,6 +381,10 @@ const (
 	// DupeResAlgRemove records all duplicate records like the 'record' algorithm and remove all information related to the
 	// duplicated rows. Users need to analyze the lightning_task_info.conflict_error_v1 table to add back the correct rows.
 	DupeResAlgRemove
+
+	// DupeResAlgErr reports an error and stops the import process.
+	// Note: this value is only used for internal.
+	DupeResAlgErr
 )
 
 func (dra *DuplicateResolutionAlgorithm) UnmarshalTOML(v interface{}) error {
diff --git a/ddl/BUILD.bazel b/ddl/BUILD.bazel
index e5ef726cfc749..6dfaedd66846f 100644
--- a/ddl/BUILD.bazel
+++ b/ddl/BUILD.bazel
@@ -52,6 +52,7 @@ go_library(
         ":ddl_friend",
     ],
     deps = [
+        "//br/pkg/lightning/common",
         "//br/pkg/utils",
         "//config",
         "//ddl/ingest",
diff --git a/ddl/index.go b/ddl/index.go
index 3a25f49e6a257..e69e1962c112b 100644
--- a/ddl/index.go
+++ b/ddl/index.go
@@ -26,6 +26,7 @@ import (
 	"github.com/pingcap/errors"
 	"github.com/pingcap/failpoint"
 	"github.com/pingcap/kvproto/pkg/kvrpcpb"
+	"github.com/pingcap/tidb/br/pkg/lightning/common"
 	"github.com/pingcap/tidb/br/pkg/utils"
 	"github.com/pingcap/tidb/config"
 	"github.com/pingcap/tidb/ddl/ingest"
@@ -38,6 +39,7 @@ import (
 	"github.com/pingcap/tidb/parser/charset"
 	"github.com/pingcap/tidb/parser/model"
 	"github.com/pingcap/tidb/parser/mysql"
+	"github.com/pingcap/tidb/parser/terror"
 	"github.com/pingcap/tidb/sessionctx"
 	"github.com/pingcap/tidb/table"
 	"github.com/pingcap/tidb/table/tables"
@@ -824,8 +826,11 @@ func doReorgWorkForCreateIndex(w *worker, d *ddlCtx, t *meta.Meta, job *model.Jo
 			}
 			err = bc.FinishImport(indexInfo.ID, indexInfo.Unique, tbl)
 			if err != nil {
-				if kv.ErrKeyExists.Equal(err) {
+				if kv.ErrKeyExists.Equal(err) || common.ErrFoundDuplicateKeys.Equal(err) {
 					logutil.BgLogger().Warn("[ddl] import index duplicate key, convert job to rollback", zap.String("job", job.String()), zap.Error(err))
+					if common.ErrFoundDuplicateKeys.Equal(err) {
+						err = convertToKeyExistsErr(err, indexInfo, tbl.Meta())
+					}
 					ver, err = convertAddIdxJob2RollbackJob(d, t, job, tbl.Meta(), indexInfo, err)
 				} else {
 					logutil.BgLogger().Warn("[ddl] lightning import error", zap.Error(err))
@@ -866,6 +871,22 @@ func doReorgWorkForCreateIndex(w *worker, d *ddlCtx, t *meta.Meta, job *model.Jo
 	}
 }
 
+func convertToKeyExistsErr(originErr error, idxInfo *model.IndexInfo, tblInfo *model.TableInfo) error {
+	tErr, ok := errors.Cause(originErr).(*terror.Error)
+	if !ok {
+		return originErr
+	}
+	if len(tErr.Args()) != 2 {
+		return originErr
+	}
+	key, keyIsByte := tErr.Args()[0].([]byte)
+	value, valIsByte := tErr.Args()[1].([]byte)
+	if !keyIsByte || !valIsByte {
+		return originErr
+	}
+	return genKeyExistsErr(key, value, idxInfo, tblInfo)
+}
+
 func runReorgJobAndHandleErr(w *worker, d *ddlCtx, t *meta.Meta, job *model.Job,
 	tbl table.Table, indexInfo *model.IndexInfo, mergingTmpIdx bool) (done bool, ver int64, err error) {
 	elements := []*meta.Element{{ID: indexInfo.ID, TypeKey: meta.IndexElementKey}}
@@ -1223,7 +1244,7 @@ func newAddIndexWorker(sessCtx sessionctx.Context, id int, t table.PhysicalTable
 		if err != nil {
 			return nil, errors.Trace(err)
 		}
-		lwCtx, err = ei.NewWriterCtx(id)
+		lwCtx, err = ei.NewWriterCtx(id, indexInfo.Unique)
 		if err != nil {
 			return nil, err
 		}
@@ -1408,17 +1429,26 @@ func (w *addIndexWorker) checkHandleExists(key kv.Key, value []byte, handle kv.H
 	if hasBeenBackFilled {
 		return nil
 	}
+	return genKeyExistsErr(key, value, idxInfo, tblInfo)
+}
+
+func genKeyExistsErr(key, value []byte, idxInfo *model.IndexInfo, tblInfo *model.TableInfo) error {
+	idxColLen := len(idxInfo.Columns)
+	indexName := fmt.Sprintf("%s.%s", tblInfo.Name.String(), idxInfo.Name.String())
 	colInfos := tables.BuildRowcodecColInfoForIndexColumns(idxInfo, tblInfo)
 	values, err := tablecodec.DecodeIndexKV(key, value, idxColLen, tablecodec.HandleNotNeeded, colInfos)
 	if err != nil {
-		return err
+		logutil.BgLogger().Warn("decode index key value failed", zap.String("index", indexName),
+			zap.String("key", hex.EncodeToString(key)), zap.String("value", hex.EncodeToString(value)), zap.Error(err))
+		return kv.ErrKeyExists.FastGenByArgs(key, indexName)
 	}
-	indexName := fmt.Sprintf("%s.%s", w.index.TableMeta().Name.String(), w.index.Meta().Name.String())
 	valueStr := make([]string, 0, idxColLen)
 	for i, val := range values[:idxColLen] {
 		d, err := tablecodec.DecodeColumnValue(val, colInfos[i].Ft, time.Local)
 		if err != nil {
-			return kv.ErrKeyExists.FastGenByArgs(key.String(), indexName)
+			logutil.BgLogger().Warn("decode column value failed", zap.String("index", indexName),
+				zap.String("key", hex.EncodeToString(key)), zap.String("value", hex.EncodeToString(value)), zap.Error(err))
+			return kv.ErrKeyExists.FastGenByArgs(key, indexName)
 		}
 		str, err := d.ToString()
 		if err != nil {
diff --git a/ddl/ingest/config.go b/ddl/ingest/config.go
index e9c1458b1ab0a..7fd251a361939 100644
--- a/ddl/ingest/config.go
+++ b/ddl/ingest/config.go
@@ -47,7 +47,7 @@ func generateLightningConfig(memRoot MemRoot, jobID int64, unique bool) (*config
 	adjustImportMemory(memRoot, cfg)
 	cfg.Checkpoint.Enable = true
 	if unique {
-		cfg.TikvImporter.DuplicateResolution = config.DupeResAlgRecord
+		cfg.TikvImporter.DuplicateResolution = config.DupeResAlgErr
 	} else {
 		cfg.TikvImporter.DuplicateResolution = config.DupeResAlgNone
 	}
diff --git a/ddl/ingest/engine.go b/ddl/ingest/engine.go
index 5bf32762dcc22..ac0287b26637a 100644
--- a/ddl/ingest/engine.go
+++ b/ddl/ingest/engine.go
@@ -17,6 +17,7 @@ package ingest
 import (
 	"context"
 	"strconv"
+	"sync/atomic"
 
 	"github.com/google/uuid"
 	"github.com/pingcap/tidb/br/pkg/lightning/backend"
@@ -42,6 +43,7 @@ type engineInfo struct {
 	writerCache  generic.SyncMap[int, *backend.LocalEngineWriter]
 	memRoot      MemRoot
 	diskRoot     DiskRoot
+	rowSeq       atomic.Int64
 }
 
 // NewEngineInfo create a new EngineInfo struct.
@@ -145,17 +147,18 @@ func (ei *engineInfo) ImportAndClean() error {
 // WriterContext is used to keep a lightning local writer for each backfill worker.
 type WriterContext struct {
 	ctx    context.Context
+	rowSeq func() int64
 	lWrite *backend.LocalEngineWriter
 }
 
-func (ei *engineInfo) NewWriterCtx(id int) (*WriterContext, error) {
+func (ei *engineInfo) NewWriterCtx(id int, unique bool) (*WriterContext, error) {
 	ei.memRoot.RefreshConsumption()
 	ok := ei.memRoot.CheckConsume(StructSizeWriterCtx)
 	if !ok {
 		return nil, genEngineAllocMemFailedErr(ei.memRoot, ei.jobID, ei.indexID)
 	}
 
-	wCtx, err := ei.newWriterContext(id)
+	wCtx, err := ei.newWriterContext(id, unique)
 	if err != nil {
 		logutil.BgLogger().Error(LitErrCreateContextFail, zap.Error(err),
 			zap.Int64("job ID", ei.jobID), zap.Int64("index ID", ei.indexID),
@@ -176,7 +179,7 @@ func (ei *engineInfo) NewWriterCtx(id int) (*WriterContext, error) {
 // If local writer not exist, then create new one and store it into engine info writer cache.
 // note: operate ei.writeCache map is not thread safe please make sure there is sync mechanism to
 // make sure the safe.
-func (ei *engineInfo) newWriterContext(workerID int) (*WriterContext, error) {
+func (ei *engineInfo) newWriterContext(workerID int, unique bool) (*WriterContext, error) {
 	lWrite, exist := ei.writerCache.Load(workerID)
 	if !exist {
 		var err error
@@ -187,10 +190,16 @@ func (ei *engineInfo) newWriterContext(workerID int) (*WriterContext, error) {
 		// Cache the local writer.
 		ei.writerCache.Store(workerID, lWrite)
 	}
-	return &WriterContext{
+	wc := &WriterContext{
 		ctx:    ei.ctx,
 		lWrite: lWrite,
-	}, nil
+	}
+	if unique {
+		wc.rowSeq = func() int64 {
+			return ei.rowSeq.Add(1)
+		}
+	}
+	return wc, nil
 }
 
 func (ei *engineInfo) closeWriters() error {
@@ -214,6 +223,9 @@ func (wCtx *WriterContext) WriteRow(key, idxVal []byte) error {
 	kvs := make([]common.KvPair, 1)
 	kvs[0].Key = key
 	kvs[0].Val = idxVal
+	if wCtx.rowSeq != nil {
+		kvs[0].RowID = wCtx.rowSeq()
+	}
 	row := kv.MakeRowsFromKvPairs(kvs)
 	return wCtx.lWrite.WriteRows(wCtx.ctx, nil, row)
 }
diff --git a/errors.toml b/errors.toml
index e675ad0bb239c..36865561a3c1e 100644
--- a/errors.toml
+++ b/errors.toml
@@ -526,6 +526,11 @@ error = '''
 encode kv error in file %s at offset %d
 '''
 
+["Lightning:Restore:ErrFoundDuplicateKey"]
+error = '''
+found duplicate key '%s', value '%s'
+'''
+
 ["Lightning:Restore:ErrInvalidMetaStatus"]
 error = '''
 invalid meta status: '%s'
diff --git a/tests/realtikvtest/addindextest/integration_test.go b/tests/realtikvtest/addindextest/integration_test.go
index 35a636bec7be4..9b79704d3e7b4 100644
--- a/tests/realtikvtest/addindextest/integration_test.go
+++ b/tests/realtikvtest/addindextest/integration_test.go
@@ -308,3 +308,29 @@ func TestAddIndexIngestPanicOnCopRead(t *testing.T) {
 	// Fallback to txn-merge process.
 	require.True(t, strings.Contains(jobTp, "txn-merge"), jobTp)
 }
+
+func TestAddIndexIngestUniqueKey(t *testing.T) {
+	store := realtikvtest.CreateMockStoreAndSetup(t)
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("drop database if exists addindexlit;")
+	tk.MustExec("create database addindexlit;")
+	tk.MustExec("use addindexlit;")
+	tk.MustExec(`set global tidb_ddl_enable_fast_reorg=on;`)
+
+	tk.MustExec("create table t (a int primary key, b int);")
+	tk.MustExec("insert into t values (1, 1), (10000, 1);")
+	tk.MustExec("split table t by (5000);")
+	tk.MustGetErrMsg("alter table t add unique index idx(b);", "[kv:1062]Duplicate entry '1' for key 't.idx'")
+
+	tk.MustExec("drop table t;")
+	tk.MustExec("create table t (a varchar(255) primary key, b int);")
+	tk.MustExec("insert into t values ('a', 1), ('z', 1);")
+	tk.MustExec("split table t by ('m');")
+	tk.MustGetErrMsg("alter table t add unique index idx(b);", "[kv:1062]Duplicate entry '1' for key 't.idx'")
+
+	tk.MustExec("drop table t;")
+	tk.MustExec("create table t (a varchar(255) primary key, b int, c char(5));")
+	tk.MustExec("insert into t values ('a', 1, 'c1'), ('d', 2, 'c1'), ('x', 1, 'c2'), ('z', 1, 'c1');")
+	tk.MustExec("split table t by ('m');")
+	tk.MustGetErrMsg("alter table t add unique index idx(b, c);", "[kv:1062]Duplicate entry '1-c1' for key 't.idx'")
+}