diff --git a/tests/test_fernet.py b/tests/test_fernet.py
index 455d985..5b7a9f9 100644
--- a/tests/test_fernet.py
+++ b/tests/test_fernet.py
@@ -7,6 +7,7 @@
 import base64
 import calendar
 import json
+import os
 import time
 
 import iso8601
@@ -24,7 +25,9 @@
 
 
 def json_parametrize(keys, filename):
-    vector_file = cryptography_vectors.open_vector_file('fernet', filename)
+    vector_file = cryptography_vectors.open_vector_file(
+        os.path.join('fernet', filename), "r"
+    )
     with vector_file:
         data = json.load(vector_file)
         return pytest.mark.parametrize(keys, [
diff --git a/tests/utils.py b/tests/utils.py
index ad38000..01ab4e6 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -87,8 +87,8 @@
     return encoder.encode(sig)
 
 
-def load_vectors_from_file(filename, loader):
-    with cryptography_vectors.open_vector_file(filename) as vector_file:
+def load_vectors_from_file(filename, loader, mode="r"):
+    with cryptography_vectors.open_vector_file(filename, mode) as vector_file:
         return loader(vector_file)
 
 
diff --git a/vectors/cryptography_vectors/__init__.py b/vectors/cryptography_vectors/__init__.py
index 34cf442..abcfe14 100644
--- a/vectors/cryptography_vectors/__init__.py
+++ b/vectors/cryptography_vectors/__init__.py
@@ -18,6 +18,6 @@
 ]
 
 
-def open_vector_file(*args):
+def open_vector_file(filename, mode):
     base = os.path.dirname(__file__)
-    return open(os.path.join(base, *args), "r")
+    return open(os.path.join(base, filename), mode)