diff --git a/python/src/trezorlib/btc.py b/python/src/trezorlib/btc.py
index 357f12f220..c5b0b1600b 100644
--- a/python/src/trezorlib/btc.py
+++ b/python/src/trezorlib/btc.py
@@ -14,7 +14,7 @@
 # You should have received a copy of the License along with this library.
 # If not, see <https://www.gnu.org/licenses/lgpl-3.0.html>.
 
-from . import coins, messages
+from . import messages
 from .tools import CallException, expect, normalize_nfc, session
 
 
@@ -88,27 +88,7 @@ def verify_message(client, coin_name, address, signature, message):
 
 @session
 def sign_tx(client, coin_name, inputs, outputs, details=None, prev_txes=None):
-    # set up a transactions dict
-    txes = {None: messages.TransactionType(inputs=inputs, outputs=outputs)}
-    # preload all relevant transactions ahead of time
-    if coin_name in coins.by_name:
-        load_prevtxes = not coins.by_name[coin_name]["force_bip143"]
-    else:
-        load_prevtxes = True
-    if load_prevtxes:
-        for inp in inputs:
-            if inp.script_type not in (
-                messages.InputScriptType.SPENDP2SHWITNESS,
-                messages.InputScriptType.SPENDWITNESS,
-                messages.InputScriptType.EXTERNAL,
-            ):
-                try:
-                    prev_tx = prev_txes[inp.prev_hash]
-                except Exception as e:
-                    raise ValueError("Could not retrieve prev_tx") from e
-                if not isinstance(prev_tx, messages.TransactionType):
-                    raise ValueError("Invalid value for prev_tx") from None
-                txes[inp.prev_hash] = prev_tx
+    this_tx = messages.TransactionType(inputs=inputs, outputs=outputs)
 
     if details is None:
         signtx = messages.SignTx()
@@ -155,7 +135,10 @@ def sign_tx(client, coin_name, inputs, outputs, details=None, prev_txes=None):
             break
 
         # Device asked for one more information, let's process it.
-        current_tx = txes[res.details.tx_hash]
+        if res.details.tx_hash is not None:
+            current_tx = prev_txes[res.details.tx_hash]
+        else:
+            current_tx = this_tx
 
         if res.request_type == R.TXMETA:
             msg = copy_tx_meta(current_tx)