diff --git a/trezorlib/tx_api.py b/trezorlib/tx_api.py
index d01a551a2..b1b86d8ae 100644
--- a/trezorlib/tx_api.py
+++ b/trezorlib/tx_api.py
@@ -12,6 +12,33 @@ except:
 
 import types_pb2 as proto_types
 
+def op_push(i):
+    if i<0x4c:
+        return chr(i)
+    elif i<0xff:
+        return '\x4c' + chr(i)
+    elif i<0xffff:
+        return '\x4d' + struct.pack("<H", i)
+    else:
+        return '\x4e' + struct.pack("<I", i)
+
+def opcode_serialize(opcode):
+    # TODO: this function supports just small subset of script for now (enough for most transactions)
+    if opcode == 'OP_DUP':
+        return '\x76'
+    if opcode == 'OP_HASH160':
+        return '\xa9'
+    if opcode == 'OP_EQUALVERIFY':
+        return '\x88'
+    if opcode == 'OP_CHECKSIG':
+        return '\xac'
+    # it's probably hex data
+    try:
+        x = binascii.unhexlify(opcode)
+        return op_push(len(x)) + x
+    except:
+        raise Exception('Unknown script opcode: %s' % opcode)
+
 def bitcore_tx(url):
     f = urllib2.urlopen(url)
     data = json.load(f)
@@ -24,17 +51,16 @@ def bitcore_tx(url):
         i = t.inputs.add()
         i.prev_hash = binascii.unhexlify(vin['txid'])
         i.prev_index = vin['vout']
-        asm = [ binascii.unhexlify(x) for x in vin['scriptSig']['asm'].split(' ') ]
-        i.script_sig = chr(len(asm[0])) + asm[0] + chr(len(asm[1])) + asm[1] # TODO: should be op_push(x) instead of chr(len(x))
+        asm = vin['scriptSig']['asm'].split(' ')
+        asm = [ opcode_serialize(x) for x in asm ]
+        i.script_sig = ''.join(asm)
 
     for vout in data['vout']:
         o = t.outputs.add()
         o.amount = int(vout['value'] * 100000000)
         asm = vout['scriptPubKey']['asm'].split(' ')
-        # we suppose it's OP_DUP OP_HASH160 pubkey OP_EQUALVERIFY OP_CHECKSIG
-        if len(asm) != 5 or asm[0] != 'OP_DUP' or asm[1] != 'OP_HASH160' or asm[3] != 'OP_EQUALVERIFY' or asm[4] != 'OP_CHECKSIG':
-            raise Exception('Unknown scriptPubKey asm: %s' % asm)
-        o.script_pubkey = binascii.unhexlify('76a914' + asm[2] + '88ac')
+        asm = [ opcode_serialize(x) for x in asm ]
+        o.script_pubkey = ''.join(asm)
 
     return t