diff --git a/setup.py b/setup.py
index 231d5cb..0e3a048 100644
--- a/setup.py
+++ b/setup.py
@@ -18,7 +18,7 @@ install_requires = [
# https://github.com/certbot/josepy/issues/13.
'josepy>=1.1.0',
# Connection.set_tlsext_host_name (>=0.13) + matching Xenial requirements (>=0.15.1)
- 'PyOpenSSL>=0.15.1',
+ 'PyOpenSSL>=0.13.1',
'pyrfc3339',
'pytz',
'requests>=2.6.0', # security extras added in 2.4.1