diff --git a/cryptography/fernet.py b/cryptography/fernet.py
index 6bc401d..4f98fee 100644
--- a/cryptography/fernet.py
+++ b/cryptography/fernet.py
@@ -131,6 +131,7 @@
 
 class MultiFernet(object):
     def __init__(self, fernets):
+        fernets = list(fernets)
         if not fernets:
             raise ValueError(
                 "MultiFernet requires at least one Fernet instance"
diff --git a/tests/test_fernet.py b/tests/test_fernet.py
index 91af32a..58f89cb 100644
--- a/tests/test_fernet.py
+++ b/tests/test_fernet.py
@@ -146,3 +146,7 @@
     def test_no_fernets(self, backend):
         with pytest.raises(ValueError):
             MultiFernet([])
+
+    def test_non_iterable_argument(self, backend):
+        with pytest.raises(TypeError):
+            MultiFernet(None)