diff -r c368e43859ba Lib/inspect.py
--- a/Lib/inspect.py	Sat Aug 24 00:42:54 2013 +0300
+++ b/Lib/inspect.py	Sun Aug 25 17:41:08 2013 +0300
@@ -789,7 +789,8 @@
             for parent in c.__bases__:
                 if not parent in children:
                     children[parent] = []
-                children[parent].append(c)
+                if c not in children[parent]:
+                    children[parent].append(c)
                 if unique and parent in classes: break
         elif c not in roots:
             roots.append(c)
diff -r c368e43859ba Lib/test/inspect_fodder.py
--- a/Lib/test/inspect_fodder.py	Sat Aug 24 00:42:54 2013 +0300
+++ b/Lib/test/inspect_fodder.py	Sun Aug 25 17:41:08 2013 +0300
@@ -49,6 +49,8 @@
 class MalodorousPervert(StupidGit):
     pass
 
+Tit = MalodorousPervert
+
 class ParrotDroppings:
     pass
 
diff -r c368e43859ba Lib/test/test_inspect.py
--- a/Lib/test/test_inspect.py	Sat Aug 24 00:42:54 2013 +0300
+++ b/Lib/test/test_inspect.py	Sun Aug 25 17:41:08 2013 +0300
@@ -225,7 +225,9 @@
                          [('FesteringGob', mod.FesteringGob),
                           ('MalodorousPervert', mod.MalodorousPervert),
                           ('ParrotDroppings', mod.ParrotDroppings),
-                          ('StupidGit', mod.StupidGit)])
+                          ('StupidGit', mod.StupidGit),
+                          ('Tit', mod.MalodorousPervert),
+                         ])
         tree = inspect.getclasstree([cls[1] for cls in classes], 1)
         self.assertEqual(tree,
                          [(object, ()),