diff --git a/cryptography/bindings/openssl/api.py b/cryptography/bindings/openssl/api.py
index 1782378..02957d7 100644
--- a/cryptography/bindings/openssl/api.py
+++ b/cryptography/bindings/openssl/api.py
@@ -72,13 +72,12 @@
         )
         evp_cipher = self._lib.EVP_get_cipherbyname(ciphername.encode("ascii"))
         assert evp_cipher != self._ffi.NULL
-        # TODO: only use the key and initialization_vector as needed. Sometimes
-        # this needs to be a DecryptInit, when?
-        iv = self._get_iv(mode)
+        iv_nonce = mode.get_iv_or_nonce(self)
 
+        # TODO: Sometimes this needs to be a DecryptInit, when?
         res = self._lib.EVP_EncryptInit_ex(
             ctx, evp_cipher, self._ffi.NULL, cipher.key,
-            iv
+            iv_nonce
         )
         assert res != 0
 
@@ -87,15 +86,8 @@
         self._lib.EVP_CIPHER_CTX_set_padding(ctx, 0)
         return ctx
 
-    def _get_iv(self, mode):
-        # TODO: refactor this to visitor pattern
-        klass_name = mode.__class__.__name__
-        if klass_name == 'CBC':
-            return mode.initialization_vector
-        elif klass_name == 'ECB':
-            return self._ffi.NULL
-        else:
-            raise NotImplementedError
+    def get_null_for_ecb(self):
+        return self._ffi.NULL
 
     def update_encrypt_context(self, ctx, plaintext):
         buf = self._ffi.new("unsigned char[]", len(plaintext))
diff --git a/cryptography/primitives/block/modes.py b/cryptography/primitives/block/modes.py
index ac3392c..8214143 100644
--- a/cryptography/primitives/block/modes.py
+++ b/cryptography/primitives/block/modes.py
@@ -21,6 +21,12 @@
         super(CBC, self).__init__()
         self.initialization_vector = initialization_vector
 
+    def get_iv_or_nonce(self, api):
+        return self.initialization_vector
+
 
 class ECB(object):
     name = "ECB"
+
+    def get_iv_or_nonce(self, api):
+        return api.get_null_for_ecb()
diff --git a/tests/bindings/test_openssl.py b/tests/bindings/test_openssl.py
index e4b7346..c5927b7 100644
--- a/tests/bindings/test_openssl.py
+++ b/tests/bindings/test_openssl.py
@@ -11,8 +11,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import pytest
-
 from cryptography.bindings.openssl import api
 
 
@@ -31,6 +29,5 @@
         """
         assert api.openssl_version_text().startswith("OpenSSL")
 
-    def test_get_iv_invalid_mode(self):
-        with pytest.raises(NotImplementedError):
-            api._get_iv(None)
+    def test_get_null_for_ecb(self):
+        assert api.get_null_for_ecb() == api._ffi.NULL