diff --git a/electrum/transaction.py b/electrum/transaction.py
index 9d971fd6f..ccb6305d0 100644
--- a/electrum/transaction.py
+++ b/electrum/transaction.py
@@ -1171,6 +1171,10 @@ class PartialTxInput(TxInput, PSBTSection):
 
     @classmethod
     def from_txin(cls, txin: TxInput, *, strip_witness: bool = True) -> 'PartialTxInput':
+        # FIXME: if strip_witness is True, res.is_segwit() will return False,
+        # and res.estimated_size() will return an incorrect value. These methods
+        # will return the correct values after we call add_input_info(). (see dscancel and bump_fee)
+        # This is very fragile: the value returned by estimate_size() depends on the calling order.
         res = PartialTxInput(prevout=txin.prevout,
                              script_sig=None if strip_witness else txin.script_sig,
                              nsequence=txin.nsequence,
diff --git a/electrum/wallet.py b/electrum/wallet.py
index 537258650..f918b1f3b 100644
--- a/electrum/wallet.py
+++ b/electrum/wallet.py
@@ -1394,12 +1394,12 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
         if tx.is_final():
             raise CannotBumpFee(_('Transaction is final'))
         new_fee_rate = quantize_feerate(new_fee_rate)  # strip excess precision
-        old_tx_size = tx.estimated_size()
         try:
             # note: this might download input utxos over network
             tx.add_info_from_wallet(self, ignore_network_issues=False)
         except NetworkException as e:
             raise CannotBumpFee(repr(e))
+        old_tx_size = tx.estimated_size()
         old_fee = tx.get_fee()
         assert old_fee is not None
         old_fee_rate = old_fee / old_tx_size  # sat/vbyte
@@ -1573,12 +1573,12 @@ class Abstract_Wallet(AddressSynchronizer, ABC):
         if tx.is_final():
             raise CannotDoubleSpendTx(_('Transaction is final'))
         new_fee_rate = quantize_feerate(new_fee_rate)  # strip excess precision
-        old_tx_size = tx.estimated_size()
         try:
             # note: this might download input utxos over network
             tx.add_info_from_wallet(self, ignore_network_issues=False)
         except NetworkException as e:
             raise CannotDoubleSpendTx(repr(e))
+        old_tx_size = tx.estimated_size()
         old_fee = tx.get_fee()
         assert old_fee is not None
         old_fee_rate = old_fee / old_tx_size  # sat/vbyte