diff --git a/checkm8.py b/checkm8.py
index a2298e9f..90b48a69 100644
--- a/checkm8.py
+++ b/checkm8.py
@@ -453,7 +453,7 @@ def exploit_config(serial_number):
     if 'SRTG:[%s]' % config.version in serial_number:
       return payload(config.cpid), config
   for config in all_exploit_configs():
-    if 'CPID:%s' % config.cpid in serial_number:
+    if 'CPID:%x' % config.cpid in serial_number:
       print 'ERROR: CPID is compatible, but serial number string does not match.'
       print 'Make sure device is in SecureROM DFU Mode and not LLB/iBSS DFU Mode. Exiting.'
       sys.exit(1)