1 files changed, 10 insertions, 1 deletions
diff --git a/tests/hazmat/primitives/test_hkdf.py b/tests/hazmat/primitives/test_hkdf.py
index e3e2a9df..963fb69c 100644
--- a/tests/hazmat/primitives/test_hkdf.py
+++ b/tests/hazmat/primitives/test_hkdf.py
@@ -17,7 +17,9 @@ import six
 
 import pytest
 
-from cryptography.exceptions import AlreadyFinalized, InvalidKey
+from cryptography.exceptions import (
+    AlreadyFinalized, InvalidKey, UnsupportedInterface
+)
 from cryptography.hazmat.primitives import hashes
 from cryptography.hazmat.primitives.kdf.hkdf import HKDF
 
@@ -145,3 +147,10 @@ class TestHKDF(object):
             )
 
             hkdf.verify(b"foo", six.u("bar"))
+
+
+def test_invalid_backend():
+    pretend_backend = object()
+
+    with pytest.raises(UnsupportedInterface):
+        HKDF(hashes.SHA256(), 16, None, None, pretend_backend)