diff --git a/opendbc_repo/opendbc/car/hyundai/hyundaicanfd.py b/opendbc_repo/opendbc/car/hyundai/hyundaicanfd.py
index 8f580c9b90..3f303912ad 100644
--- a/opendbc_repo/opendbc/car/hyundai/hyundaicanfd.py
+++ b/opendbc_repo/opendbc/car/hyundai/hyundaicanfd.py
@@ -1,10 +1,10 @@
 import math
+from binascii import crc_hqx
 from typing import cast
 
 import numpy as np
 from opendbc.car import CanBusBase, CanData
 from opendbc.car.common.conversions import Conversions as CV
-from opendbc.car.crc import CRC16_XMODEM
 from opendbc.car.hyundai.ioniq6_bsm import BlindspotStatus, FRONT_NEUTRAL_BODY, rear_body
 from opendbc.car.hyundai.values import CAR, HyundaiFlags
 
@@ -437,11 +437,7 @@ def create_adrv_messages(packer, CAN, frame, *, template=None, drive_gear=False,
 
 
 def hkg_can_fd_checksum(address: int, sig, d: bytearray) -> int:
-  crc = 0
-  for i in range(2, len(d)):
-    crc = ((crc << 8) ^ CRC16_XMODEM[(crc >> 8) ^ d[i]]) & 0xFFFF
-  crc = ((crc << 8) ^ CRC16_XMODEM[(crc >> 8) ^ ((address >> 0) & 0xFF)]) & 0xFFFF
-  crc = ((crc << 8) ^ CRC16_XMODEM[(crc >> 8) ^ ((address >> 8) & 0xFF)]) & 0xFFFF
+  crc = crc_hqx(d[2:] + (address & 0xFFFF).to_bytes(2, "little"), 0)
   if len(d) == 8:
     crc ^= 0x5F29
   elif len(d) == 16:
diff --git a/opendbc_repo/opendbc/car/hyundai/tests/test_canfd_checksum.py b/opendbc_repo/opendbc/car/hyundai/tests/test_canfd_checksum.py
new file mode 100644
index 0000000000..0446ef085e
--- /dev/null
+++ b/opendbc_repo/opendbc/car/hyundai/tests/test_canfd_checksum.py
@@ -0,0 +1,63 @@
+import unittest
+
+from opendbc.car.hyundai.hyundaicanfd import hkg_can_fd_checksum
+
+
+def reference_checksum(address, data):
+  crc = 0
+  for byte in (*data[2:], address & 0xFF, (address >> 8) & 0xFF):
+    for bit in range(7, -1, -1):
+      feedback = (crc >> 15) ^ ((byte >> bit) & 1)
+      crc = (crc << 1) & 0xFFFF
+      if feedback:
+        crc ^= 0x1021
+  return crc ^ {8: 0x5F29, 16: 0x041D, 24: 0x819D, 32: 0x9F5B}.get(len(data), 0)
+
+
+class TestCanfdChecksum(unittest.TestCase):
+  def test_matches_bitwise_reference_and_preserves_input(self):
+    addresses = (0, 1, 0x1234, 0x7FE, 0x7FF, 0x800, 0x801,
+                 0xFFFE, 0xFFFF, 0x10000, 0x10001,
+                 0x1FFFFFFE, 0x1FFFFFFF, 0x20000000,
+                 -1, -0x10001, (1 << 160) | 0x1234)
+    for length in range(65):
+      payloads = (bytes(length), b"\xff" * length,
+                  bytes((i * 37 + length * 13) & 0xFF for i in range(length)))
+      for pattern, payload in enumerate(payloads):
+        for address in addresses:
+          expected = reference_checksum(address, payload)
+          for container in (bytes, bytearray):
+            with self.subTest(length=length, pattern=pattern, address=address, container=container.__name__):
+              data = container(payload)
+              self.assertEqual(hkg_can_fd_checksum(address, None, data), expected)
+              self.assertEqual(data, payload)
+
+  def test_first_two_bytes_are_ignored(self):
+    for length in range(65):
+      payload = bytes((i * 29 + 17) & 0xFF for i in range(length))
+      expected = reference_checksum(0x1234, payload)
+      for prefix in (b"\x00\x00", b"\xff\xff", b"\x5a\xa5"):
+        for container in (bytes, bytearray):
+          with self.subTest(length=length, prefix=prefix, container=container.__name__):
+            data = container(prefix[:min(2, length)] + payload[2:])
+            self.assertEqual(hkg_can_fd_checksum(0x1234, None, data), expected)
+
+  def test_only_low_sixteen_address_bits_are_used(self):
+    for length in range(65):
+      payload = bytes((i * 19 + 3) & 0xFF for i in range(length))
+      for low_address in (0, 0x7FF, 0x800, 0x1234, 0xFFFF):
+        expected = reference_checksum(low_address, payload)
+        for address in (low_address - (1 << 80), low_address | (1 << 160)):
+          for container in (bytes, bytearray):
+            with self.subTest(length=length, address=address, container=container.__name__):
+              self.assertEqual(hkg_can_fd_checksum(address, None, container(payload)), expected)
+
+  def test_zero_payload_length_adjustments(self):
+    for length, expected in ((0, 0), (1, 0), (2, 0), (8, 0x5F29),
+                             (16, 0x041D), (24, 0x819D), (32, 0x9F5B), (64, 0)):
+      with self.subTest(length=length):
+        self.assertEqual(hkg_can_fd_checksum(0, None, bytes(length)), expected)
+
+
+if __name__ == "__main__":
+  unittest.main()
diff --git a/prebuilt.json b/prebuilt.json
index cbd114bc53..b89086b43e 100644
--- a/prebuilt.json
+++ b/prebuilt.json
@@ -1 +1 @@
-{"protected_inventory_sha256": "ec474989597c90246eef09acaacab24b8bbf68c04b1271dbac521e005b84082a", "schema_version": 1}
+{"protected_inventory_sha256": "13836c06f15783e9b64f424907c835e5acde61997c1c6a106f8037ee6560fded", "schema_version": 1}