diff --git a/executor/adapter.go b/executor/adapter.go
index 1caf36fddd773..430dae026582b 100644
--- a/executor/adapter.go
+++ b/executor/adapter.go
@@ -733,7 +733,7 @@ func (a *ExecStmt) handlePessimisticDML(ctx context.Context, e Executor) error {
 		if err1 != nil {
 			return err1
 		}
-		keys = txnCtx.CollectUnchangedRowKeys(keys)
+		keys = txnCtx.CollectUnchangedLockKeys(keys)
 		if len(keys) == 0 {
 			return nil
 		}
diff --git a/executor/write.go b/executor/write.go
index 2c9c8fe4107fa..397ec2669a46d 100644
--- a/executor/write.go
+++ b/executor/write.go
@@ -158,7 +158,21 @@ func updateRecord(ctx context.Context, sctx sessionctx.Context, h kv.Handle, old
 		unchangedRowKey := tablecodec.EncodeRowKeyWithHandle(physicalID, h)
 		txnCtx := sctx.GetSessionVars().TxnCtx
 		if txnCtx.IsPessimistic {
-			txnCtx.AddUnchangedRowKey(unchangedRowKey)
+			txnCtx.AddUnchangedLockKey(unchangedRowKey)
+			for _, idx := range t.Indices() {
+				if !idx.Meta().Unique {
+					continue
+				}
+				ukVals, err := idx.FetchValues(oldData, nil)
+				if err != nil {
+					return false, err
+				}
+				unchangedUniqueKey, _, err := idx.GenIndexKey(sc, ukVals, h, nil)
+				if err != nil {
+					return false, err
+				}
+				txnCtx.AddUnchangedLockKey(unchangedUniqueKey)
+			}
 		}
 		return false, nil
 	}
diff --git a/sessionctx/variable/session.go b/sessionctx/variable/session.go
index ddf249281858a..05e2c059fb45f 100644
--- a/sessionctx/variable/session.go
+++ b/sessionctx/variable/session.go
@@ -169,8 +169,9 @@ type TxnCtxNoNeedToRestore struct {
 	currentShard int64
 	shardRand    *rand.Rand
 
-	// unchangedRowKeys is used to store the unchanged rows that needs to lock for pessimistic transaction.
-	unchangedRowKeys map[string]struct{}
+	// unchangedLockKeys is used to store the unchanged keys that needs to lock for pessimistic transaction, including
+	// row keys and unique keys.
+	unchangedLockKeys map[string]struct{}
 
 	PessimisticCacheHit int
 
@@ -239,20 +240,20 @@ func (tc *TransactionContext) updateShard() {
 	tc.currentShard = int64(murmur3.Sum32(buf[:]))
 }
 
-// AddUnchangedRowKey adds an unchanged row key in update statement for pessimistic lock.
-func (tc *TransactionContext) AddUnchangedRowKey(key []byte) {
-	if tc.unchangedRowKeys == nil {
-		tc.unchangedRowKeys = map[string]struct{}{}
+// AddUnchangedLockKey adds an unchanged key in update statement for pessimistic lock.
+func (tc *TransactionContext) AddUnchangedLockKey(key []byte) {
+	if tc.unchangedLockKeys == nil {
+		tc.unchangedLockKeys = map[string]struct{}{}
 	}
-	tc.unchangedRowKeys[string(key)] = struct{}{}
+	tc.unchangedLockKeys[string(key)] = struct{}{}
 }
 
-// CollectUnchangedRowKeys collects unchanged row keys for pessimistic lock.
-func (tc *TransactionContext) CollectUnchangedRowKeys(buf []kv.Key) []kv.Key {
-	for key := range tc.unchangedRowKeys {
+// CollectUnchangedLockKeys collects unchanged keys for pessimistic lock.
+func (tc *TransactionContext) CollectUnchangedLockKeys(buf []kv.Key) []kv.Key {
+	for key := range tc.unchangedLockKeys {
 		buf = append(buf, kv.Key(key))
 	}
-	tc.unchangedRowKeys = nil
+	tc.unchangedLockKeys = nil
 	return buf
 }
 
diff --git a/tests/realtikvtest/pessimistictest/pessimistic_test.go b/tests/realtikvtest/pessimistictest/pessimistic_test.go
index 58bb2b73a86f5..1759fff3e3bd4 100644
--- a/tests/realtikvtest/pessimistictest/pessimistic_test.go
+++ b/tests/realtikvtest/pessimistictest/pessimistic_test.go
@@ -503,6 +503,38 @@ func TestLockUnchangedRowKey(t *testing.T) {
 	tk2.MustExec("rollback")
 }
 
+func TestLockUnchangedUniqueKey(t *testing.T) {
+	store, clean := realtikvtest.CreateMockStoreAndSetup(t)
+	defer clean()
+
+	tk := testkit.NewTestKit(t, store)
+	tk2 := testkit.NewTestKit(t, store)
+	tk.MustExec("use test")
+	tk2.MustExec("use test")
+
+	// ref https://github.com/pingcap/tidb/issues/36438
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t (i varchar(10), unique key(i))")
+	tk.MustExec("insert into t values ('a')")
+	tk.MustExec("begin pessimistic")
+	tk.MustExec("update t set i = 'a'")
+
+	errCh := make(chan error, 1)
+	go func() {
+		_, err := tk2.Exec("insert into t values ('a')")
+		errCh <- err
+	}()
+
+	select {
+	case <-errCh:
+		require.Fail(t, "insert is not blocked by update")
+	case <-time.After(500 * time.Millisecond):
+		tk.MustExec("rollback")
+	}
+
+	require.Error(t, <-errCh)
+}
+
 func TestOptimisticConflicts(t *testing.T) {
 	store, clean := realtikvtest.CreateMockStoreAndSetup(t)
 	defer clean()