diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
index 4b2d055..6f6e96f 100644
--- a/Lib/test/test_unicode.py
+++ b/Lib/test/test_unicode.py
@@ -1142,6 +1142,15 @@
         self.assertRaises(MemoryError, alloc)
         self.assertRaises(MemoryError, alloc)
 
+    def test_format_subclass(self):
+        class U(unicode):
+            def __unicode__(self):
+                return u'__unicode__ overridden'
+        u = U(u'xxx')
+        self.assertEquals("%s" % u, u'__unicode__ overridden')
+        self.assertEquals("{0}".format(u), u'__unicode__ overridden')
+
+
 def test_main():
     test_support.run_unittest(__name__)