diff --git a/python/uds.py b/python/uds.py
index 5bf35088e..c95074a45 100644
--- a/python/uds.py
+++ b/python/uds.py
@@ -457,6 +457,9 @@ class IsoTpMessage():
         print(f"ISO-TP: RESPONSE - {hex(self._can_client.rx_addr)} 0x{bytes.hex(self.rx_dat)}")
 
   def _isotp_rx_next(self, rx_data: bytes) -> None:
+    # ISO 15765-2 specifies an eight byte CAN frame for ISO-TP communication
+    assert len(rx_data) == 8, f"isotp - rx: invalid CAN frame length: {len(rx_data)}"
+
     # single rx_frame
     if rx_data[0] >> 4 == 0x0:
       self.rx_len = rx_data[0] & 0xFF