diff --git a/scrapy/xpath/document.py b/scrapy/xpath/document.py
index 78fb58306..308342cdb 100644
--- a/scrapy/xpath/document.py
+++ b/scrapy/xpath/document.py
@@ -10,6 +10,7 @@ from scrapy.xpath.factories import xmlDoc_from_html
 class Libxml2Document(object):
 
     cache = weakref.WeakKeyDictionary()
+    __slots__ = ['xmlDoc', 'xpathContext']
 
     def __new__(cls, response, factory=xmlDoc_from_html):
         cache = cls.cache.setdefault(response, {})
diff --git a/scrapy/xpath/selector.py b/scrapy/xpath/selector.py
index 67c272e35..993e158f5 100644
--- a/scrapy/xpath/selector.py
+++ b/scrapy/xpath/selector.py
@@ -16,6 +16,8 @@ from scrapy.utils.decorator import deprecated
 
 class XPathSelector(object_ref):
 
+    __slots__ = ['doc', 'xmlNode', 'response', 'expr']
+
     def __init__(self, response=None, text=None, node=None, parent=None, expr=None):
         if parent:
             self.doc = parent.doc