diff --git a/Tools/scripts/signing/make_secure_bl.py b/Tools/scripts/signing/make_secure_bl.py
index e3ed4718a4..bd60bee3c7 100755
--- a/Tools/scripts/signing/make_secure_bl.py
+++ b/Tools/scripts/signing/make_secure_bl.py
@@ -36,7 +36,7 @@ offset += 8
 desc = b''
 desc_len = 0
 
-keys = args.keys[:]
+keys = []
 
 if not args.omit_ardupilot_keys:
     print("Adding ArduPilot keys")
@@ -47,6 +47,8 @@ if not args.omit_ardupilot_keys:
             if f.endswith(".dat"):
                 keys.append(os.path.relpath(os.path.join(keydir, f)))
 
+keys += args.keys[:]
+
 if len(keys) > max_keys:
     print("Too many key files %u, max is %u" % (len(keys), max_keys))
     sys.exit(1)