diff --git a/letsencrypt/cli.py b/letsencrypt/cli.py
index d343fcaa5..7227116e3 100644
--- a/letsencrypt/cli.py
+++ b/letsencrypt/cli.py
@@ -107,7 +107,7 @@ def _find_domains(args, installer):
 
     if not domains:
         raise errors.Error("Please specify --domains, or --installer that "
-                    "will help in domain names autodiscovery")
+                           "will help in domain names autodiscovery")
 
     return domains
 
@@ -1085,7 +1085,6 @@ def main(cli_args=sys.argv[1:]):
     # note: arg parser internally handles --help (and exits afterwards)
     plugins = plugins_disco.PluginsRegistry.find_all()
     args = prepare_and_parse_args(plugins, cli_args)
-    # Check command line parameters sanity, and error out in case of problem.
     config = configuration.NamespaceConfig(args)
     zope.component.provideUtility(config)
 
diff --git a/letsencrypt/configuration.py b/letsencrypt/configuration.py
index 8fa3cb2dc..e70171675 100644
--- a/letsencrypt/configuration.py
+++ b/letsencrypt/configuration.py
@@ -37,6 +37,7 @@ class NamespaceConfig(object):
 
     def __init__(self, namespace):
         self.namespace = namespace
+        # Check command line parameters sanity, and error out in case of problem.
         check_config_sanity(self)
 
     def __getattr__(self, name):
@@ -120,7 +121,7 @@ def check_config_sanity(config):
     """
     # Port check
     if config.http01_port == config.tls_sni_01_port:
-        raise errors.Error(
+        raise errors.ConfigurationError(
             "Trying to run http-01 and tls-sni-01 "
             "on the same port ({0})".format(config.tls_sni_01_port))
 
@@ -134,7 +135,9 @@ def _check_config_domain_sanity(domains):
     domain flag values and errors out if the requirements are not met.
 
     :param domains: List of domains
-    :type args: `list` of `string`
+    :type domains: `list` of `string`
+    :raises ConfigurationError: for invalid domains and cases where Let's
+                                Encrypt currently will not issue certificates
 
     """
     # Check if there's a wildcard domain
@@ -145,8 +148,10 @@ def _check_config_domain_sanity(domains):
     if any("xn--" in d for d in domains):
         raise errors.ConfigurationError(
             "Punycode domains are not supported")
-    # FQDN, checks:
+    # FQDN checks from
+    # http://www.mkyong.com/regular-expressions/domain-name-regular-expression-example/
     #  Characters used, domain parts < 63 chars, tld > 1 < 7 chars
+    #  first and last char is not "-"
     fqdn = re.compile("^((?!-)[A-Za-z0-9-]{1,63}(?<!-)\\.)+[A-Za-z]{2,6}$")
     if any(True for d in domains if not fqdn.match(d)):
-        raise errors.ConfigurationError("Requested domain is not FQDN")
+        raise errors.ConfigurationError("Requested domain is not a FQDN")
diff --git a/letsencrypt/errors.py b/letsencrypt/errors.py
index 252358bdf..0df544b0d 100644
--- a/letsencrypt/errors.py
+++ b/letsencrypt/errors.py
@@ -95,5 +95,6 @@ class StandaloneBindError(Error):
         self.socket_error = socket_error
         self.port = port
 
+
 class ConfigurationError(Error):
     """Configuration sanity error."""