diff --git a/docs/hazmat/backends/interfaces.rst b/docs/hazmat/backends/interfaces.rst
index 14ca688..975a7b0 100644
--- a/docs/hazmat/backends/interfaces.rst
+++ b/docs/hazmat/backends/interfaces.rst
@@ -136,6 +136,8 @@
 
 .. class:: PBKDF2Backend
 
+    .. versionadded:: 0.2
+
     A backend with methods for using PBKDF2.
 
     .. method:: pbkdf2_hash_supported(algorithm)
@@ -157,7 +159,7 @@
             provider.
 
         :param int length: The desired length of the derived key. Maximum is
-        2\ :sup:`31` - 1.
+            2\ :sup:`31` - 1.
 
         :param bytes salt: A salt.
 
diff --git a/docs/hazmat/primitives/index.rst b/docs/hazmat/primitives/index.rst
index 2a29bd8..bde0739 100644
--- a/docs/hazmat/primitives/index.rst
+++ b/docs/hazmat/primitives/index.rst
@@ -9,7 +9,7 @@
     cryptographic-hashes
     hmac
     symmetric-encryption
-    key-derivation-functions
     padding
+    key-derivation-functions
     constant-time
     interfaces
diff --git a/docs/hazmat/primitives/key-derivation-functions.rst b/docs/hazmat/primitives/key-derivation-functions.rst
index af2d910..51d73bc 100644
--- a/docs/hazmat/primitives/key-derivation-functions.rst
+++ b/docs/hazmat/primitives/key-derivation-functions.rst
@@ -10,8 +10,16 @@
 
 .. class:: PBKDF2(algorithm, length, salt, iterations, backend):
 
+    .. versionadded:: 0.2
+
+    This class conforms to the
+    :class:`~cryptography.hazmat.primitives.interfaces.KeyDerivationFunction`
+    interface.
+
     .. doctest::
 
+        >>> import os
+        >>> from cryptography.hazmat.primitives import hashes
         >>> from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2
         >>> from cryptography.hazmat.backends import default_backend
         >>> backend = default_backend()
@@ -22,19 +30,18 @@
         >>> # verify
         >>> kdf = PBKDF2(hashes.SHA1(), 20, salt, 10000, backend)
         >>> kdf.verify(b"my great password", key)
-        None
 
-        :param algorithm: An instance of a
-            :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
-            provider.
-
-        :param int length: The desired length of the derived key. Maximum is
+    :param algorithm: An instance of a
+        :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
+        provider.
+    :param int length: The desired length of the derived key. Maximum is
         2\ :sup:`31` - 1.
-
-        :param bytes salt: A salt. `NIST SP 800-132`_ recommends 128-bits or
-            longer.
-
-        :param int iterations: The number of iterations to perform of the hash
-            function.
+    :param bytes salt: A salt. `NIST SP 800-132`_ recommends 128-bits or
+        longer.
+    :param int iterations: The number of iterations to perform of the hash
+        function.
+    :param backend: A
+        :class:`~cryptography.hazmat.backends.interfaces.CipherBackend`
+        provider.
 
 .. _`NIST SP 800-132`: http://csrc.nist.gov/publications/nistpubs/800-132/nist-sp800-132.pdf