diff --git a/ddl/index_merge_tmp.go b/ddl/index_merge_tmp.go
index 5f699b3507e6f..a7b9816fc85de 100644
--- a/ddl/index_merge_tmp.go
+++ b/ddl/index_merge_tmp.go
@@ -59,6 +59,15 @@ func (w *mergeIndexWorker) batchCheckTemporaryUniqueKey(txn kv.Transaction, idxR
 			}
 			if !idxRecords[i].delete {
 				idxRecords[i].skip = true
+			} else {
+				// Prevent deleting an unexpected index KV.
+				hdInVal, err := tablecodec.DecodeHandleInUniqueIndexValue(val, w.table.Meta().IsCommonHandle)
+				if err != nil {
+					return errors.Trace(err)
+				}
+				if !idxRecords[i].handle.Equal(hdInVal) {
+					idxRecords[i].skip = true
+				}
 			}
 		} else if idxRecords[i].distinct {
 			// The keys in w.batchCheckKeys also maybe duplicate,
@@ -76,6 +85,7 @@ type temporaryIndexRecord struct {
 	delete   bool
 	unique   bool
 	distinct bool
+	handle   kv.Handle
 	rowKey   kv.Key
 }
 
@@ -137,7 +147,8 @@ func (w *mergeIndexWorker) BackfillDataInTxn(taskRange reorgBackfillTask) (taskC
 
 			// Lock the corresponding row keys so that it doesn't modify the index KVs
 			// that are changing by a pessimistic transaction.
-			err := txn.LockKeys(context.Background(), new(kv.LockCtx), idxRecord.rowKey)
+			rowKey := tablecodec.EncodeRecordKey(w.table.RecordPrefix(), idxRecord.handle)
+			err := txn.LockKeys(context.Background(), new(kv.LockCtx), rowKey)
 			if err != nil {
 				return errors.Trace(err)
 			}
@@ -209,14 +220,13 @@ func (w *mergeIndexWorker) fetchTempIndexVals(txn kv.Transaction, taskRange reor
 					return false, err
 				}
 			}
-			rowKey := tablecodec.EncodeRecordKey(w.table.RecordPrefix(), handle)
 
 			originIdxKey := make([]byte, len(indexKey))
 			copy(originIdxKey, indexKey)
 			tablecodec.TempIndexKey2IndexKey(w.index.Meta().ID, originIdxKey)
 
 			idxRecord := &temporaryIndexRecord{
-				rowKey: rowKey,
+				handle: handle,
 				delete: isDelete,
 				unique: unique,
 				skip:   false,
diff --git a/ddl/index_merge_tmp_test.go b/ddl/index_merge_tmp_test.go
index 6027c5cee215f..1c4d107a0aebf 100644
--- a/ddl/index_merge_tmp_test.go
+++ b/ddl/index_merge_tmp_test.go
@@ -378,6 +378,43 @@ func TestAddIndexMergeIndexUpdateOnDeleteOnly(t *testing.T) {
 	tk.MustExec("admin check table t;")
 }
 
+func TestAddIndexMergeDeleteUniqueOnWriteOnly(t *testing.T) {
+	store, dom := testkit.CreateMockStoreAndDomain(t)
+
+	tk := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk.MustExec("create table t(a int default 0, b int default 0);")
+	tk.MustExec("insert into t values (1, 1), (2, 2), (3, 3), (4, 4);")
+
+	tk1 := testkit.NewTestKit(t, store)
+	tk1.MustExec("use test")
+
+	d := dom.DDL()
+	originalCallback := d.GetHook()
+	defer d.SetHook(originalCallback)
+	callback := &ddl.TestDDLCallback{}
+	onJobUpdatedExportedFunc := func(job *model.Job) {
+		if t.Failed() {
+			return
+		}
+		var err error
+		switch job.SchemaState {
+		case model.StateDeleteOnly:
+			_, err = tk1.Exec("insert into t values (5, 5);")
+			assert.NoError(t, err)
+		case model.StateWriteOnly:
+			_, err = tk1.Exec("insert into t values (5, 7);")
+			assert.NoError(t, err)
+			_, err = tk1.Exec("delete from t where b = 7;")
+			assert.NoError(t, err)
+		}
+	}
+	callback.OnJobUpdatedExported.Store(&onJobUpdatedExportedFunc)
+	d.SetHook(callback)
+	tk.MustExec("alter table t add unique index idx(a);")
+	tk.MustExec("admin check table t;")
+}
+
 func TestAddIndexMergeConflictWithPessimistic(t *testing.T) {
 	store, dom := testkit.CreateMockStoreAndDomain(t)
 	tk := testkit.NewTestKit(t, store)