diff --git a/can/tests/test_packer_parser.py b/can/tests/test_packer_parser.py
index 79f24ec5aa..c313805c47 100755
--- a/can/tests/test_packer_parser.py
+++ b/can/tests/test_packer_parser.py
@@ -382,6 +382,18 @@ def test_disallow_duplicate_messages(self):
     with self.assertRaises(RuntimeError):
       CANParser("toyota_nodsu_pt_generated", [("ACC_CONTROL", 10), ("ACC_CONTROL", 10)])
 
+  def test_allow_undefined_msgs(self):
+    # TODO: we should throw an exception for these, but we need good
+    #  discovery tests in openpilot first
+    packer = CANPacker("toyota_nodsu_pt_generated")
+
+    self.assertEqual(packer.make_can_msg("ACC_CONTROL", 0, {"UNKNOWN_SIGNAL": 0}),
+                     [835, 0, b'\x00\x00\x00\x00\x00\x00\x00N', 0])
+    self.assertEqual(packer.make_can_msg("UNKNOWN_MESSAGE", 0, {"UNKNOWN_SIGNAL": 0}),
+                     [0, 0, b'', 0])
+    self.assertEqual(packer.make_can_msg(0, 0, {"UNKNOWN_SIGNAL": 0}),
+                     [0, 0, b'', 0])
+
 
 if __name__ == "__main__":
   unittest.main()