diff --git a/src/cryptography/hazmat/primitives/asymmetric/rsa.py b/src/cryptography/hazmat/primitives/asymmetric/rsa.py
index 3157aed..27db671 100644
--- a/src/cryptography/hazmat/primitives/asymmetric/rsa.py
+++ b/src/cryptography/hazmat/primitives/asymmetric/rsa.py
@@ -5,7 +5,11 @@
 from __future__ import absolute_import, division, print_function
 
 import abc
-from fractions import gcd
+try:
+    # Only available in math in 3.5+
+    from math import gcd
+except ImportError:
+    from fractions import gcd
 
 import six