diff --git a/lib/transaction.py b/lib/transaction.py
index f4f359b6e..55014e2cb 100644
--- a/lib/transaction.py
+++ b/lib/transaction.py
@@ -612,14 +612,41 @@ class Transaction:
         else:
             raise TypeError('Unknown output type')
 
+    @classmethod
+    def estimate_pubkey_size_from_x_pubkey(cls, x_pubkey):
+        try:
+            if x_pubkey[0:2] in ['02', '03']:  # compressed pubkey
+                return 0x21
+            elif x_pubkey[0:2] == '04':  # uncompressed pubkey
+                return 0x41
+            elif x_pubkey[0:2] == 'ff':  # bip32 extended pubkey
+                return 0x21
+            elif x_pubkey[0:2] == 'fe':  # old electrum extended pubkey
+                return 0x41
+        except Exception as e:
+            pass
+        return 0x21  # just guess it is compressed
+
+    @classmethod
+    def estimate_pubkey_size_for_txin(cls, txin):
+        pubkeys = txin.get('pubkeys', [])
+        x_pubkeys = txin.get('x_pubkeys', [])
+        if len(pubkeys) > 0:
+            return cls.estimate_pubkey_size_from_x_pubkey(pubkeys[0])
+        elif len(x_pubkeys) > 0:
+            return cls.estimate_pubkey_size_from_x_pubkey(x_pubkeys[0])
+        else:
+            return 0x21  # just guess it is compressed
+
     @classmethod
     def get_siglist(self, txin, estimate_size=False):
         # if we have enough signatures, we use the actual pubkeys
         # otherwise, use extended pubkeys (with bip32 derivation)
         num_sig = txin.get('num_sig', 1)
         if estimate_size:
+            pubkey_size = self.estimate_pubkey_size_for_txin(txin)
+            pk_list = ["00" * pubkey_size] * num_sig
             # we assume that signature will be 0x48 bytes long
-            pk_list = [ "00" * 0x21 ] * num_sig
             sig_list = [ "00" * 0x48 ] * num_sig
         else:
             pubkeys, x_pubkeys = self.get_sorted_pubkeys(txin)