diff --git a/letsencrypt/client/client.py b/letsencrypt/client/client.py
index d939022ed..a4e98fa41 100644
--- a/letsencrypt/client/client.py
+++ b/letsencrypt/client/client.py
@@ -63,7 +63,7 @@ class Client(object):
 
         # TODO: Allow for other alg types besides RS256
         self.network = network2.Network(
-            "https://" + config.server, jwk.JWKRSA.load(self.account.key.pem))
+            config.server_url, jwk.JWKRSA.load(self.account.key.pem))
 
         self.config = config
 
diff --git a/letsencrypt/client/configuration.py b/letsencrypt/client/configuration.py
index df00ee3aa..14c7b23cd 100644
--- a/letsencrypt/client/configuration.py
+++ b/letsencrypt/client/configuration.py
@@ -28,6 +28,8 @@ class NamespaceConfig(object):
     zope.interface.implements(interfaces.IConfig)
 
     def __init__(self, namespace):
+        assert not namespace.server.startswith('https://')
+        assert not namespace.server.startswith('http://')
         self.namespace = namespace
 
     def __getattr__(self, name):
@@ -42,24 +44,32 @@ class NamespaceConfig(object):
     def in_progress_dir(self):  # pylint: disable=missing-docstring
         return os.path.join(self.namespace.work_dir, constants.IN_PROGRESS_DIR)
 
+    @property
+    def server_path(self):
+        """File path based on ``server``."""
+        return self.namespace.server.replace('/', os.path.sep)
+
+    @property
+    def server_url(self):
+        """Full server URL (including HTTPS scheme)."""
+        return 'https://' + self.namespace.server
+
     @property
     def cert_key_backup(self):  # pylint: disable=missing-docstring
         return os.path.join(
             self.namespace.work_dir, constants.CERT_KEY_BACKUP_DIR,
-            self.namespace.server.partition(":")[0])
+            self.server_path)
 
     @property
     def accounts_dir(self):  #pylint: disable=missing-docstring
         return os.path.join(
-            self.namespace.config_dir, constants.ACCOUNTS_DIR,
-            self.namespace.server.replace(':', '-').replace('/', '-'))
+            self.namespace.config_dir, constants.ACCOUNTS_DIR, self.server_path)
 
     @property
     def account_keys_dir(self):  #pylint: disable=missing-docstring
         return os.path.join(
             self.namespace.config_dir, constants.ACCOUNTS_DIR,
-            self.namespace.server.replace(':', '-').replace('/', '-'),
-            constants.ACCOUNT_KEYS_DIR)
+            self.server_path, constants.ACCOUNT_KEYS_DIR)
 
     # TODO: This should probably include the server name
     @property