diff --git a/cryptography/primitives/block/base.py b/cryptography/primitives/block/base.py
index 197807e..b84ca9c 100644
--- a/cryptography/primitives/block/base.py
+++ b/cryptography/primitives/block/base.py
@@ -24,8 +24,12 @@
 
 
 class BlockCipher(object):
-    def __init__(self, cipher, mode, api=_default_api):
+    def __init__(self, cipher, mode, api=None):
         super(BlockCipher, self).__init__()
+
+        if api is None:
+            api = _default_api
+
         self.cipher = cipher
         self.mode = mode
         self._api = api
diff --git a/tests/primitives/test_block.py b/tests/primitives/test_block.py
index 92fd31a..774885f 100644
--- a/tests/primitives/test_block.py
+++ b/tests/primitives/test_block.py
@@ -31,6 +31,13 @@
         )
         assert cipher.name == "AES-128-CBC"
 
+    def test_instantiate_without_api(self):
+        cipher = BlockCipher(
+            ciphers.AES(binascii.unhexlify(b"0" * 32)),
+            modes.CBC(binascii.unhexlify(b"0" * 32))
+        )
+        assert cipher.name == "AES-128-CBC"
+
     def test_use_after_finalize(self, api):
         cipher = BlockCipher(
             ciphers.AES(binascii.unhexlify(b"0" * 32)),
diff --git a/tox.ini b/tox.ini
index 88e7421..0a28af1 100644
--- a/tox.ini
+++ b/tox.ini
@@ -8,7 +8,7 @@
     pretend
 commands =
     coverage run --source=cryptography/,tests/ -m pytest
-    coverage report
+    coverage report -m
 
 [testenv:docs]
 deps = sphinx