=== modified file 'Objects/setobject.c'
--- Objects/setobject.c	2010-05-09 13:46:46 +0000
+++ Objects/setobject.c	2010-05-11 08:48:38 +0000
@@ -1523,6 +1523,7 @@
 set_difference(PySetObject *so, PyObject *other)
 {
     PyObject *result;
+    PySetObject *tmp;
     setentry *entry;
     Py_ssize_t pos = 0;
 
@@ -1555,6 +1556,12 @@
         return result;
     }
 
+    if (set_len((PyObject *)so) > set_len(other)) {
+	tmp = so;
+	so = (PySetObject *)other;
+	other = (PyObject *)tmp;
+    }
+
     while (set_next(so, &pos, &entry)) {
         int rv = set_contains_entry((PySetObject *)other, entry);
         if (rv == -1) {