Fixed #809 -- switch back to always using UnsupportedAlgorithm
diff --git a/docs/hazmat/primitives/key-derivation-functions.rst b/docs/hazmat/primitives/key-derivation-functions.rst
index 6196d95..269f949 100644
--- a/docs/hazmat/primitives/key-derivation-functions.rst
+++ b/docs/hazmat/primitives/key-derivation-functions.rst
@@ -84,7 +84,7 @@
         :class:`~cryptography.hazmat.backends.interfaces.PBKDF2HMACBackend`
         provider.
 
-    :raises cryptography.exceptions.UnsupportedInterface: This is raised if the
+    :raises cryptography.exceptions.UnsupportedAlgorithm: This is raised if the
         provided ``backend`` does not implement
         :class:`~cryptography.hazmat.backends.interfaces.PBKDF2HMACBackend`
 
@@ -187,7 +187,7 @@
         :class:`~cryptography.hazmat.backends.interfaces.HMACBackend`
         provider.
 
-    :raises cryptography.exceptions.UnsupportedInterface: This is raised if the
+    :raises cryptography.exceptions.UnsupportedAlgorithm: This is raised if the
         provided ``backend`` does not implement
         :class:`~cryptography.hazmat.backends.interfaces.HMACBackend`