diff --git a/letsencrypt/client/plugins/nginx/configurator.py b/letsencrypt/client/plugins/nginx/configurator.py
index 38006e742..7fed3f9a2 100644
--- a/letsencrypt/client/plugins/nginx/configurator.py
+++ b/letsencrypt/client/plugins/nginx/configurator.py
@@ -290,7 +290,7 @@ class NginxConfigurator(object):
                 self.choose_vhost(domain), options)
         except (KeyError, ValueError):
             raise errors.LetsEncryptConfiguratorError(
-                "Unsupported enhancement: {}".format(enhancement))
+                "Unsupported enhancement: {0}".format(enhancement))
         except errors.LetsEncryptConfiguratorError:
             logging.warn("Failed %s for %s", enhancement, domain)