diff --git a/store/tikv/2pc.go b/store/tikv/2pc.go
index 5d2eee2e9519d..41daf9a23394a 100644
--- a/store/tikv/2pc.go
+++ b/store/tikv/2pc.go
@@ -341,7 +341,16 @@ func (c *twoPhaseCommitter) initKeysAndMutations() error {
 		} else {
 			value = it.Value()
 			if len(value) > 0 {
-				if tablecodec.IsUntouchedIndexKValue(key, value) {
+				isUntouchedValue := tablecodec.IsUntouchedIndexKValue(key, value)
+				if isUntouchedValue {
+					if flags.HasPresumeKeyNotExists() {
+						logutil.BgLogger().Error("unexpected path the untouched key value with PresumeKeyNotExists flag",
+							zap.Stringer("key", key), zap.Stringer("value", kv.Key(value)),
+							zap.Uint16("flags", uint16(flags)), zap.Stack("stack"))
+						return errors.Errorf(
+							"unexpected path the untouched key=%s value=%s contains PresumeKeyNotExists flag keyFlags=%v",
+							key.String(), kv.Key(value).String(), flags)
+					}
 					if !flags.HasLocked() {
 						continue
 					}
diff --git a/table/tables/index.go b/table/tables/index.go
index 08f37f1e984b4..0a63019373b4a 100644
--- a/table/tables/index.go
+++ b/table/tables/index.go
@@ -172,8 +172,22 @@ func (c *index) Create(sctx sessionctx.Context, txn kv.Transaction, indexedValue
 		// should not overwrite the key with un-commit flag.
 		// So if the key exists, just do nothing and return.
 		v, err := txn.GetMemBuffer().Get(ctx, key)
-		if err == nil && len(v) != 0 {
-			return nil, nil
+		if err == nil {
+			if len(v) != 0 {
+				return nil, nil
+			}
+			// The key is marked as deleted in the memory buffer, as the existence check is done lazily
+			// for optimistic transactions by default. The "untouched" key could still exist in the store,
+			// it's needed to commit this key to do the existence check so unset the untouched flag.
+			if !txn.IsPessimistic() {
+				keyFlags, err := txn.GetMemBuffer().GetFlags(key)
+				if err != nil {
+					return nil, err
+				}
+				if keyFlags.HasPresumeKeyNotExists() {
+					opt.Untouched = false
+				}
+			}
 		}
 	}
 
diff --git a/table/tables/tables_test.go b/table/tables/tables_test.go
index 9b7df03bb33d1..f2b5d7442660f 100644
--- a/table/tables/tables_test.go
+++ b/table/tables/tables_test.go
@@ -746,3 +746,29 @@ func (ts *testSuite) TestViewColumns(c *C) {
 			"Warning|1356|View 'test.va' references invalid table(s) or column(s) or function(s) or definer/invoker of view lack rights to use them"))
 	}
 }
+
+func (ts *testSuite) TestConstraintCheckForOptimisticUntouched(c *C) {
+	se, err := session.CreateSession4Test(ts.store)
+	c.Assert(err, IsNil)
+	c.Assert(se.Auth(&auth.UserIdentity{Username: "root", Hostname: "%"}, nil, nil), IsTrue)
+	tk := testkit.NewTestKitWithSession(c, ts.store, se)
+
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists test_optimistic_untouched_flag;")
+	tk.MustExec(`create table test_optimistic_untouched_flag(c0 int, c1 varchar(20), c2 varchar(20), unique key uk(c0));`)
+	tk.MustExec(`insert into test_optimistic_untouched_flag(c0, c1, c2) values (1, null, 'green');`)
+
+	// Insert a row with duplicated entry on the unique key, the commit should fail.
+	tk.MustExec("begin optimistic;")
+	tk.MustExec(`insert into test_optimistic_untouched_flag(c0, c1, c2) values (1, 'red', 'white');`)
+	tk.MustExec(`delete from test_optimistic_untouched_flag where c1 is null;`)
+	tk.MustExec("update test_optimistic_untouched_flag set c2 = 'green' where c2 between 'purple' and 'white';")
+	err = tk.ExecToErr("commit")
+	c.Assert(err, NotNil)
+
+	tk.MustExec("begin optimistic;")
+	tk.MustExec(`insert into test_optimistic_untouched_flag(c0, c1, c2) values (1, 'red', 'white');`)
+	tk.MustExec("update test_optimistic_untouched_flag set c2 = 'green' where c2 between 'purple' and 'white';")
+	err = tk.ExecToErr("commit")
+	c.Assert(err, NotNil)
+}