diff --git a/cryptography/bindings/__init__.py b/cryptography/bindings/__init__.py
index b4dc6bf..8b16500 100644
--- a/cryptography/bindings/__init__.py
+++ b/cryptography/bindings/__init__.py
@@ -14,4 +14,4 @@
 from cryptography.bindings.openssl import api
 
 
-default_api = api
+_default_api = api
diff --git a/cryptography/primitives/block/base.py b/cryptography/primitives/block/base.py
index 833ebe9..197807e 100644
--- a/cryptography/primitives/block/base.py
+++ b/cryptography/primitives/block/base.py
@@ -15,7 +15,7 @@
 
 from enum import Enum
 
-from cryptography.bindings import default_api
+from cryptography.bindings import _default_api
 
 
 class _Operation(Enum):
@@ -24,7 +24,7 @@
 
 
 class BlockCipher(object):
-    def __init__(self, cipher, mode, api=default_api):
+    def __init__(self, cipher, mode, api=_default_api):
         super(BlockCipher, self).__init__()
         self.cipher = cipher
         self.mode = mode