diff --git a/cryptography/hazmat/bindings/__init__.py b/cryptography/hazmat/bindings/__init__.py
index eb82899..bd15819 100644
--- a/cryptography/hazmat/bindings/__init__.py
+++ b/cryptography/hazmat/bindings/__init__.py
@@ -14,7 +14,10 @@
 from cryptography.hazmat.bindings import openssl
 
 
-_default_backend = openssl.backend
 _ALL_BACKENDS = [
     openssl.backend
 ]
+
+
+def default_backend():
+    return openssl.backend
diff --git a/docs/hazmat/primitives/cryptographic-hashes.rst b/docs/hazmat/primitives/cryptographic-hashes.rst
index 52e8770..b3db9f1 100644
--- a/docs/hazmat/primitives/cryptographic-hashes.rst
+++ b/docs/hazmat/primitives/cryptographic-hashes.rst
@@ -5,7 +5,7 @@
 
 .. currentmodule:: cryptography.hazmat.primitives.hashes
 
-.. class:: Hash(algorithm)
+.. class:: Hash(algorithm, backend)
 
     A cryptographic hash function takes an arbitrary block of data and
     calculates a fixed-size bit string (a digest), such that different data
@@ -19,9 +19,9 @@
     various message digests.
 
     .. doctest::
-
+        >>> from cryptography.hazmat.bindings import default_backend
         >>> from cryptography.hazmat.primitives import hashes
-        >>> digest = hashes.Hash(hashes.SHA256())
+        >>> digest = hashes.Hash(hashes.SHA256(), default_backend())
         >>> digest.update(b"abc")
         >>> digest.update(b"123")
         >>> digest.finalize()
diff --git a/docs/hazmat/primitives/hmac.rst b/docs/hazmat/primitives/hmac.rst
index cff2dbf..7d87ca7 100644
--- a/docs/hazmat/primitives/hmac.rst
+++ b/docs/hazmat/primitives/hmac.rst
@@ -15,7 +15,7 @@
 secret key. You can use an HMAC to verify integrity as well as authenticate a
 message.
 
-.. class:: HMAC(key, algorithm)
+.. class:: HMAC(key, algorithm, backend)
 
     HMAC objects take a ``key`` and a provider of
     :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`.
@@ -27,8 +27,9 @@
 
     .. doctest::
 
+        >>> from cryptography.hazmat.bindings import default_backend
         >>> from cryptography.hazmat.primitives import hashes, hmac
-        >>> h = hmac.HMAC(key, hashes.SHA256())
+        >>> h = hmac.HMAC(key, hashes.SHA256(), default_backend())
         >>> h.update(b"message to hash")
         >>> h.finalize()
         '#F\xdaI\x8b"e\xc4\xf1\xbb\x9a\x8fc\xff\xf5\xdex.\xbc\xcd/+\x8a\x86\x1d\x84\'\xc3\xa6\x1d\xd8J'
diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst
index eef359d..42d2090 100644
--- a/docs/hazmat/primitives/symmetric-encryption.rst
+++ b/docs/hazmat/primitives/symmetric-encryption.rst
@@ -12,6 +12,9 @@
     key = binascii.unhexlify(b"0" * 32)
     iv = binascii.unhexlify(b"0" * 32)
 
+    from cryptography.hazmat.bindings import default_backend
+    backend = default_backend()
+
 
 Symmetric encryption is a way to encrypt (hide the plaintext value) material
 where the sender and receiver both use the same key. Note that symmetric
@@ -22,7 +25,7 @@
 message authentication code, such as :doc:`HMAC </hazmat/primitives/hmac>`, in
 an "encrypt-then-MAC" formulation as `described by Colin Percival`_.
 
-.. class:: Cipher(algorithm, mode)
+.. class:: Cipher(algorithm, mode, backend)
 
     Cipher objects combine an algorithm (such as
     :class:`~cryptography.hazmat.primitives.ciphers.algorithms.AES`) with a
@@ -33,8 +36,8 @@
 
     .. doctest::
 
-        >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
-        >>> cipher = Cipher(algorithms.AES(key), modes.CBC(iv))
+        >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, mode
+        >>> cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend)
         >>> encryptor = cipher.encryptor()
         >>> ct = encryptor.update(b"a secret message") + encryptor.finalize()
         >>> decryptor = cipher.decryptor()