diff --git a/example/example20.py b/example/example20.py
index c581cf3..e0a0018 100644
--- a/example/example20.py
+++ b/example/example20.py
@@ -1,16 +1,20 @@
 #!/usr/bin/env python
 from __future__ import print_function
 
+import unittest
 import numpy as np
 from example import (
     create_rec_simple, create_rec_packed, create_rec_nested, print_format_descriptors,
-    print_rec_simple, print_rec_packed, print_rec_nested, print_dtypes
+    print_rec_simple, print_rec_packed, print_rec_nested, print_dtypes, get_format_unbound
 )
 
 
 def check_eq(arr, data, dtype):
     np.testing.assert_equal(arr, np.array(data, dtype=dtype))
 
+unittest.TestCase().assertRaisesRegex(
+    RuntimeError, 'unsupported buffer format', get_format_unbound)
+
 print_format_descriptors()
 print_dtypes()