diff --git a/btclib/alias.py b/btclib/alias.py
index ea0e2dd1..0712dc45 100644
--- a/btclib/alias.py
+++ b/btclib/alias.py
@@ -73,6 +73,7 @@
 # Hash digest constructor: it may be any name suitable to hashlib.new()
 HashF = Callable[[], Any]
 # HashF = Callable[[Any], Any]
+H160_Net = Tuple[bytes, str]
 
 # Elliptic curve point in affine coordinates.
 # Warning: to make Point a NamedTuple would slow down the code
@@ -97,3 +98,10 @@
 # of the INF Point
 # QJ = Q[0], Q[1], 1 if Q[1] else 0
 INFJ = 7, 0, 0
+
+# TODO add type hinting to script_tree
+# unfortunately recursive type hinting is not supported
+# https://github.com/python/mypy/issues/731
+# TaprootLeaf = Tuple[int, Script]
+# TaprootScriptTree = List[Union[Any, TaprootLeaf]]
+TaprootScriptTree = Any
diff --git a/btclib/b32.py b/btclib/b32.py
index 0211a959..0a337f66 100644
--- a/btclib/b32.py
+++ b/btclib/b32.py
@@ -46,12 +46,12 @@
 
 from typing import Iterable
 
-from btclib.alias import Octets, String
+from btclib.alias import Octets, String, TaprootScriptTree
 from btclib.bech32 import decode, encode
 from btclib.exceptions import BTClibValueError
 from btclib.hashes import hash160, sha256
 from btclib.network import NETWORKS, network_from_key_value
-from btclib.script import TaprootScriptTree, output_pubkey
+from btclib.script import output_pubkey
 from btclib.to_pub_key import Key, pub_keyinfo_from_key
 from btclib.utils import bytes_from_octets
 
diff --git a/btclib/hashes.py b/btclib/hashes.py
index 595bec94..28bb1611 100644
--- a/btclib/hashes.py
+++ b/btclib/hashes.py
@@ -12,13 +12,11 @@
 from __future__ import annotations
 
 import hashlib
-from typing import Callable, Sequence, Tuple
+from typing import Callable, Sequence
 
 from btclib.alias import HashF, Octets
 from btclib.utils import bytes_from_octets
 
-H160_Net = Tuple[bytes, str]
-
 # see https://bugs.python.org/issue47101
 # With OpenSSL 3.x, hashlib still includes ripemd160
 # but it is not usable unless the legacy provider is loaded.
diff --git a/btclib/psbt/psbt.py b/btclib/psbt/psbt.py
index dbd6d81d..b64481c2 100644
--- a/btclib/psbt/psbt.py
+++ b/btclib/psbt/psbt.py
@@ -101,12 +101,12 @@ def __init__(
 
     def assert_valid(self) -> None:
         """Assert logical self-consistency."""
-        self.tx.assert_valid()
-
         # ensure a non-null tx has been included
         if not (self.tx.vin and self.tx.vout):
             raise BTClibValueError("null transaction")
 
+        self.tx.assert_valid()
+
         # ensure the tx is unsigned
         if any(tx_in.script_sig or tx_in.script_witness for tx_in in self.tx.vin):
             raise BTClibValueError("non empty script_sig or witness")
diff --git a/btclib/script/__init__.py b/btclib/script/__init__.py
index 958e5c0a..803d59a3 100644
--- a/btclib/script/__init__.py
+++ b/btclib/script/__init__.py
@@ -11,7 +11,17 @@
 """Module btclib.script."""
 
 from btclib.script.script import Command, Script, op_int, parse, serialize
-from btclib.script.script_pub_key import (
+from btclib.script.taproot import (
+    TaprootScriptTree,
+    check_output_pubkey,
+    input_script_sig,
+    output_prvkey,
+    output_pubkey,
+)
+from btclib.script.witness import Witness
+
+# hack to prevent circular import
+from btclib.script.script_pub_key import (  # isort:skip
     ScriptPubKey,
     address,
     assert_nulldata,
@@ -31,14 +41,7 @@
     is_p2wsh,
     type_and_payload,
 )
-from btclib.script.taproot import (
-    TaprootScriptTree,
-    check_output_pubkey,
-    input_script_sig,
-    output_prvkey,
-    output_pubkey,
-)
-from btclib.script.witness import Witness
+
 
 __all__ = [
     "Command",
diff --git a/btclib/script/taproot.py b/btclib/script/taproot.py
index 09a3d1f1..31dc11a9 100644
--- a/btclib/script/taproot.py
+++ b/btclib/script/taproot.py
@@ -16,7 +16,7 @@
 from typing import Any
 
 from btclib import var_bytes
-from btclib.alias import Octets
+from btclib.alias import Octets, TaprootScriptTree
 from btclib.ec import Curve, mult, secp256k1
 from btclib.exceptions import BTClibValueError
 from btclib.hashes import tagged_hash
@@ -25,13 +25,6 @@
 from btclib.to_pub_key import Key, pub_keyinfo_from_key
 from btclib.utils import bytes_from_octets
 
-# TODO add type hinting to script_tree
-# unfortunately recursive type hinting is not supported
-# https://github.com/python/mypy/issues/731
-# TaprootLeaf = Tuple[int, Script]
-# TaprootScriptTree = List[Union[Any, TaprootLeaf]]
-TaprootScriptTree = Any
-
 
 def tree_helper(script_tree: TaprootScriptTree) -> tuple[Any, bytes]:
     if len(script_tree) == 1:
diff --git a/btclib/tx/tx.py b/btclib/tx/tx.py
index 0d7545a8..dc2d0569 100644
--- a/btclib/tx/tx.py
+++ b/btclib/tx/tx.py
@@ -36,7 +36,7 @@
 from btclib.alias import BinaryData
 from btclib.exceptions import BTClibValueError
 from btclib.hashes import hash256
-from btclib.script import Witness
+from btclib.script.witness import Witness
 from btclib.tx.tx_in import TX_IN_COMPARES_WITNESS, TxIn
 from btclib.tx.tx_out import TxOut
 from btclib.utils import bytesio_from_binarydata
@@ -193,9 +193,13 @@ def assert_valid(self) -> None:
         if not 0 <= self.lock_time <= 0xFFFFFFFF:
             raise BTClibValueError(f"invalid lock time: {self.lock_time}")
 
+        if not self.vin:
+            raise BTClibValueError("Missing inputs")
         for tx_in in self.vin:
             tx_in.assert_valid()
 
+        if not self.vout:
+            raise BTClibValueError("Missing outputs")
         for tx_out in self.vout:
             tx_out.assert_valid()
 
diff --git a/tests/tx/test_tx.py b/tests/tx/test_tx.py
index 4e10cdab..55a1443d 100644
--- a/tests/tx/test_tx.py
+++ b/tests/tx/test_tx.py
@@ -22,7 +22,7 @@
 
 def test_tx() -> None:
     # default constructor
-    tx = Tx()
+    tx = Tx(check_validity=False)
     assert not tx.is_segwit()
     assert not any(bool(w) for w in tx.vwitness)
     assert not any(bool(tx_in.script_witness) for tx_in in tx.vin)
@@ -40,15 +40,22 @@ def test_tx() -> None:
     assert tx.vsize == tx.size
     assert tx.weight == tx.size * 4
 
-    tx_2 = Tx.from_dict(tx.to_dict())
+    with pytest.raises(BTClibValueError, match="Missing inputs"):
+        tx.assert_valid()
+
+    tx_2 = Tx.from_dict(tx.to_dict(check_validity=False), check_validity=False)
     assert tx_2.is_segwit() == tx.is_segwit()
     assert tx_2 == tx
 
-    tx_2 = Tx.parse(tx.serialize(include_witness=True))
+    tx_2 = Tx.parse(
+        tx.serialize(include_witness=True, check_validity=False), check_validity=False
+    )
     assert tx_2.is_segwit() == tx.is_segwit()
     assert tx_2 == tx
 
-    tx_2 = Tx.parse(tx.serialize(include_witness=False))
+    tx_2 = Tx.parse(
+        tx.serialize(include_witness=False, check_validity=False), check_validity=False
+    )
     assert not tx_2.is_segwit()
     assert tx_2 == tx
 
@@ -60,6 +67,10 @@ def test_tx() -> None:
     sequence = 0xFFFFFFFF
     tx_in = TxIn(prev_out, script_sig, sequence)
 
+    tx.vin = [tx_in]
+    with pytest.raises(BTClibValueError, match="Missing outputs"):
+        tx.assert_valid()
+
     tx_out1 = TxOut(2500000, "a914f987c321394968be164053d352fc49763b2be55c87")
     tx_out2 = TxOut(
         6381891, "0020701a8d401c84fb13e6baf169d59684e17abd9fa216c8cc5b9fc63d622ff8c58d"