diff --git a/docs/hazmat/primitives/cryptographic-hashes.rst b/docs/hazmat/primitives/cryptographic-hashes.rst
index f05b45a..92f8fa3 100644
--- a/docs/hazmat/primitives/cryptographic-hashes.rst
+++ b/docs/hazmat/primitives/cryptographic-hashes.rst
@@ -22,7 +22,7 @@
 
         >>> from cryptography.hazmat.bindings import default_backend
         >>> from cryptography.hazmat.primitives import hashes
-        >>> digest = hashes.Hash(hashes.SHA256(), default_backend())
+        >>> digest = hashes.Hash(hashes.SHA256(), backend=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 7d87ca7..10db40e 100644
--- a/docs/hazmat/primitives/hmac.rst
+++ b/docs/hazmat/primitives/hmac.rst
@@ -29,7 +29,7 @@
 
         >>> from cryptography.hazmat.bindings import default_backend
         >>> from cryptography.hazmat.primitives import hashes, hmac
-        >>> h = hmac.HMAC(key, hashes.SHA256(), default_backend())
+        >>> h = hmac.HMAC(key, hashes.SHA256(), backend=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 e7d019d..76f68a1 100644
--- a/docs/hazmat/primitives/symmetric-encryption.rst
+++ b/docs/hazmat/primitives/symmetric-encryption.rst
@@ -37,7 +37,7 @@
     .. doctest::
 
         >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
-        >>> cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend)
+        >>> cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=backend)
         >>> encryptor = cipher.encryptor()
         >>> ct = encryptor.update(b"a secret message") + encryptor.finalize()
         >>> decryptor = cipher.decryptor()
@@ -179,7 +179,7 @@
 
         >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
         >>> algorithm = algorithms.ARC4(key)
-        >>> cipher = Cipher(algorithm, mode=None)
+        >>> cipher = Cipher(algorithm, mode=None, backend=backend)
         >>> encryptor = cipher.encryptor()
         >>> ct = encryptor.update(b"a secret message")
         >>> decryptor = cipher.decryptor()