diff --git a/certbot/crypto_util.py b/certbot/crypto_util.py
index 942f8502f..7b558b060 100644
--- a/certbot/crypto_util.py
+++ b/certbot/crypto_util.py
@@ -458,8 +458,12 @@ def sha256sum(filename):
     :rtype: str
     """
     sha256 = hashlib.sha256()
-    with open(filename, 'rU') as file_d:
-        sha256.update(file_d.read().encode('UTF-8'))
+    if six.PY2:
+        with open(filename, 'rU') as file_d:
+            sha256.update(file_d.read().encode('UTF-8'))
+    else:
+        with open(filename, 'r', newline=None) as file_d:
+            sha256.update(file_d.read().encode('UTF-8'))
     return sha256.hexdigest()
 
 def cert_and_chain_from_fullchain(fullchain_pem):