diff --git a/python/libxml.py b/python/libxml.py
index 4c9fe92..988a166 100644
--- a/python/libxml.py
+++ b/python/libxml.py
@@ -1,10 +1,20 @@
 import libxml2mod
 import types
+import sys
 
 # The root of all libxml2 errors.
 class libxmlError(Exception): pass
 
 #
+# id() is sometimes negative ...
+#
+def pos_id(o):
+    i = id(o)
+    if (i < 0):
+        return (sys.maxint - i)
+    return i
+
+#
 # Errors raised by the wrappers when some tree handling failed.
 #
 class treeError(libxmlError):