diff --git a/pglast/ast.py b/pglast/ast.py
index bd2c0c9..5834fea 100644
--- a/pglast/ast.py
+++ b/pglast/ast.py
@@ -58,7 +58,7 @@ def __repr__(self):
 class Node:
     "Base class for all AST nodes."
 
-    __slots__ = ()
+    __slots__ = ('ancestors',)
 
     def __init__(self, data):
         if not isinstance(data, dict):  # pragma: no cover
@@ -141,7 +141,7 @@ def __setattr__(self, name, value):
         attribute, raising opportune exception when that is not possible.
         '''
 
-        if value is not None:
+        if value is not None and name in self.__slots__:
             ctype, ptype, adaptor = self.__slots__[name]
             if not isinstance(ptype, tuple):
                 ptype = (ptype,)
diff --git a/pglast/stream.py b/pglast/stream.py
index 12beb3d..ff08b40 100644
--- a/pglast/stream.py
+++ b/pglast/stream.py
@@ -11,8 +11,8 @@
 from re import match
 from sys import stderr
 
-from . import parse_plpgsql, parse_sql
 from .node import List, Missing, Node, Scalar
+from . import ast, parse_plpgsql, parse_sql, visitors
 from .keywords import RESERVED_KEYWORDS, TYPE_FUNC_NAME_KEYWORDS
 from .printers import get_printer_for_node_tag, get_special_function
 
@@ -176,6 +176,12 @@ def __call__(self, sql, plpgsql=False):
                              " a node.Node instance, a node.List, an ast.Node or tuple of"
                              " them, got %r" % type(sql))
 
+        class UpdateAncestors(visitors.Visitor):
+            def visit(self, ancestors, node):
+                node.ancestors = ancestors
+
+        UpdateAncestors()(sql)
+
         first = True
         for statement in sql:
             if first:
diff --git a/tools/extract_ast.py b/tools/extract_ast.py
index 0832d9e..88f5159 100644
--- a/tools/extract_ast.py
+++ b/tools/extract_ast.py
@@ -78,7 +78,7 @@ def __repr__(self):
 class Node:
     "Base class for all AST nodes."
 
-    __slots__ = ()
+    __slots__ = ('ancestors',)
 
     def __init__(self, data):
         if not isinstance(data, dict):  # pragma: no cover
@@ -161,7 +161,7 @@ def __setattr__(self, name, value):
         attribute, raising opportune exception when that is not possible.
         '''
 
-        if value is not None:
+        if value is not None and name in self.__slots__:
             ctype, ptype, adaptor = self.__slots__[name]
             if not isinstance(ptype, tuple):
                 ptype = (ptype,)