diff --git a/Lib/ldap/cidict.py b/Lib/ldap/cidict.py
index 3dcfe48..cf13388 100644
--- a/Lib/ldap/cidict.py
+++ b/Lib/ldap/cidict.py
@@ -15,6 +15,7 @@ class cidict(MutableMapping):
     """
     Case-insensitive but case-respecting dictionary.
     """
+    __slots__ = ('_keys', '_data')
 
     def __init__(self, default=None):
         self._keys = {}
diff --git a/Lib/ldapurl.py b/Lib/ldapurl.py
index 7ed1d8a..ecfc539 100644
--- a/Lib/ldapurl.py
+++ b/Lib/ldapurl.py
@@ -137,6 +137,7 @@ class LDAPUrlExtensions(MutableMapping):
     Models a collection of LDAP URL extensions as
     a mapping type
     """
+    __slots__ = ('_data', )
 
     def __init__(self, default=None):
         self._data = {}