diff --git a/cli/server/server.go b/cli/server/server.go
index 8aba05454..3f090cbda 100644
--- a/cli/server/server.go
+++ b/cli/server/server.go
@@ -423,7 +423,7 @@ func mkP2PNotary(config config.P2PNotary, chain *core.Blockchain, serv *network.
 	}
 	n, err := notary.NewNotary(cfg, serv.Net, serv.GetNotaryPool(), func(tx *transaction.Transaction) error {
 		err := serv.RelayTxn(tx)
-		if err != nil && !errors.Is(err, core.ErrAlreadyExists) {
+		if err != nil && !errors.Is(err, core.ErrAlreadyExists) && !errors.Is(err, core.ErrAlreadyInPool) {
 			return fmt.Errorf("can't relay completed notary transaction: hash %s, error: %w", tx.Hash().StringLE(), err)
 		}
 		return nil
diff --git a/pkg/core/blockchain.go b/pkg/core/blockchain.go
index b5ca036dd..bd28047e4 100644
--- a/pkg/core/blockchain.go
+++ b/pkg/core/blockchain.go
@@ -88,10 +88,12 @@ const (
 )
 
 var (
-	// ErrAlreadyExists is returned when trying to add some already existing
-	// transaction into the pool (not specifying whether it exists in the
-	// chain or mempool).
-	ErrAlreadyExists = errors.New("already exists")
+	// ErrAlreadyExists is returned when trying to add some transaction
+	// that already exists on chain.
+	ErrAlreadyExists = errors.New("already exists in blockchain")
+	// ErrAlreadyInPool is returned when trying to add some already existing
+	// transaction into the mempool.
+	ErrAlreadyInPool = errors.New("already exists in mempool")
 	// ErrOOM is returned when adding transaction to the memory pool because
 	// it reached its full capacity.
 	ErrOOM = errors.New("no space left in the memory pool")
@@ -2480,7 +2482,7 @@ func (bc *Blockchain) verifyAndPoolTx(t *transaction.Transaction, pool *mempool.
 	if err := bc.dao.HasTransaction(t.Hash(), t.Signers); err != nil {
 		switch {
 		case errors.Is(err, dao.ErrAlreadyExists):
-			return fmt.Errorf("blockchain: %w", ErrAlreadyExists)
+			return ErrAlreadyExists
 		case errors.Is(err, dao.ErrHasConflicts):
 			return fmt.Errorf("blockchain: %w", ErrHasConflicts)
 		default:
@@ -2500,7 +2502,7 @@ func (bc *Blockchain) verifyAndPoolTx(t *transaction.Transaction, pool *mempool.
 		case errors.Is(err, mempool.ErrConflict):
 			return ErrMemPoolConflict
 		case errors.Is(err, mempool.ErrDup):
-			return fmt.Errorf("mempool: %w", ErrAlreadyExists)
+			return ErrAlreadyInPool
 		case errors.Is(err, mempool.ErrInsufficientFunds):
 			return ErrInsufficientFunds
 		case errors.Is(err, mempool.ErrOOM):
diff --git a/pkg/core/blockchain_neotest_test.go b/pkg/core/blockchain_neotest_test.go
index c00f4b0e9..d636ce2b5 100644
--- a/pkg/core/blockchain_neotest_test.go
+++ b/pkg/core/blockchain_neotest_test.go
@@ -1358,7 +1358,7 @@ func TestBlockchain_VerifyTx(t *testing.T) {
 		require.NoError(t, bc.PoolTx(tx))
 
 		err := bc.PoolTx(tx)
-		require.ErrorIs(t, err, core.ErrAlreadyExists)
+		require.ErrorIs(t, err, core.ErrAlreadyInPool)
 	})
 	t.Run("MemPoolOOM", func(t *testing.T) {
 		mp := mempool.New(1, 0, false, nil)