diff --git a/test/functional/interface_rest.py b/test/functional/interface_rest.py
--- a/test/functional/interface_rest.py
+++ b/test/functional/interface_rest.py
@@ -4,7 +4,7 @@
 # file COPYING or http://www.opensource.org/licenses/mit-license.php.
 """Test the REST API."""
 
-from codecs import encode
+import binascii
 from decimal import Decimal
 from enum import Enum
 import http.client
@@ -13,11 +13,11 @@
 from struct import pack, unpack
 import urllib.parse
 
-from test_framework.messages import deser_uint256
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.util import (
     assert_equal,
     assert_greater_than,
+    assert_greater_than_or_equal,
     hex_str_to_bytes,
 )
 
@@ -139,8 +139,6 @@
         self.log.info(
             "Query the TXOs using the /getutxos URI with a binary response")
 
-        bb_hash = self.nodes[0].getbestblockhash()
-
         bin_request = b'\x01\x02'
         for txid, n in [spending, spent]:
             bin_request += hex_str_to_bytes(txid)
@@ -148,11 +146,9 @@
 
         bin_response = self.test_rest_request(
             "/getutxos", http_method='POST', req_type=ReqType.BIN, body=bin_request, ret_type=RetType.BYTES)
-        output = BytesIO()
-        output.write(bin_response)
-        output.seek(0)
-        chain_height = unpack("i", output.read(4))[0]
-        response_hash = hex(deser_uint256(output))[2:].zfill(64)
+        output = BytesIO(bin_response)
+        chain_height, = unpack("i", output.read(4))
+        response_hash = binascii.hexlify(output.read(32)[::-1]).decode('ascii')
 
         # Check if getutxo's chaintip during calculation was fine
         assert_equal(bb_hash, response_hash)
@@ -220,37 +216,36 @@
         self.sync_all()
 
         self.log.info("Test the /block and /headers URIs")
+        bb_hash = self.nodes[0].getbestblockhash()
 
         # Check binary format
         response = self.test_rest_request(
             "/block/{}".format(bb_hash), req_type=ReqType.BIN, ret_type=RetType.OBJ)
         assert_greater_than(int(response.getheader('content-length')), 80)
-        response_str = response.read()
+        response_bytes = response.read()
 
         # Compare with block header
         response_header = self.test_rest_request(
             "/headers/1/{}".format(bb_hash), req_type=ReqType.BIN, ret_type=RetType.OBJ)
         assert_equal(int(response_header.getheader('content-length')), 80)
-        response_header_str = response_header.read()
-        assert_equal(response_str[0:80], response_header_str)
+        response_header_bytes = response_header.read()
+        assert_equal(response_bytes[0:80], response_header_bytes)
 
         # Check block hex format
         response_hex = self.test_rest_request(
             "/block/{}".format(bb_hash), req_type=ReqType.HEX, ret_type=RetType.OBJ)
         assert_greater_than(int(response_hex.getheader('content-length')), 160)
-        response_hex_str = response_hex.read()
-        assert_equal(
-            encode(response_str, "hex_codec")[0:160], response_hex_str[0:160])
+        response_hex_bytes = response_hex.read().strip(b'\n')
+        assert_equal(binascii.hexlify(response_bytes), response_hex_bytes)
 
         # Compare with hex block header
         response_header_hex = self.test_rest_request(
             "/headers/1/{}".format(bb_hash), req_type=ReqType.HEX, ret_type=RetType.OBJ)
         assert_greater_than(
             int(response_header_hex.getheader('content-length')), 160)
-        response_header_hex_str = response_header_hex.read()
-        assert_equal(response_hex_str[0:160], response_header_hex_str[0:160])
-        assert_equal(encode(response_header_str, "hex_codec")[
-                     0:160], response_header_hex_str[0:160])
+        response_header_hex_bytes = response_header_hex.read(160)
+        assert_equal(binascii.hexlify(
+            response_bytes[:80]), response_header_hex_bytes)
 
         # Check json format
         block_json_obj = self.test_rest_request("/block/{}".format(bb_hash))
@@ -284,7 +279,8 @@
         # Check hex format response
         hex_response = self.test_rest_request(
             "/tx/{}".format(tx_hash), req_type=ReqType.HEX, ret_type=RetType.OBJ)
-        assert_greater_than(int(hex_response.getheader('content-length')), 10)
+        assert_greater_than_or_equal(
+            int(hex_response.getheader('content-length')), json_obj['size']*2)
 
         self.log.info("Test tx inclusion in the /mempool and /block URIs")