diff -r 340f45374cf5 Lib/inspect.py
--- a/Lib/inspect.py	Thu Aug 29 12:37:28 2013 +0300
+++ b/Lib/inspect.py	Thu Aug 29 13:04:36 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 340f45374cf5 Lib/test/inspect_fodder.py
--- a/Lib/test/inspect_fodder.py	Thu Aug 29 12:37:28 2013 +0300
+++ b/Lib/test/inspect_fodder.py	Thu Aug 29 13:04:36 2013 +0300
@@ -49,6 +49,8 @@
 class MalodorousPervert(StupidGit):
     pass
 
+Tit = MalodorousPervert
+
 class ParrotDroppings:
     pass
 
diff -r 340f45374cf5 Lib/test/test_inspect.py
--- a/Lib/test/test_inspect.py	Thu Aug 29 12:37:28 2013 +0300
+++ b/Lib/test/test_inspect.py	Thu Aug 29 13:04:36 2013 +0300
@@ -225,8 +225,25 @@
                          [('FesteringGob', mod.FesteringGob),
                           ('MalodorousPervert', mod.MalodorousPervert),
                           ('ParrotDroppings', mod.ParrotDroppings),
-                          ('StupidGit', mod.StupidGit)])
-        tree = inspect.getclasstree([cls[1] for cls in classes], 1)
+                          ('StupidGit', mod.StupidGit),
+                          ('Tit', mod.MalodorousPervert),
+                         ])
+        tree = inspect.getclasstree([cls[1] for cls in classes])
+        self.assertEqual(tree,
+                         [(object, ()),
+                          [(mod.ParrotDroppings, (object,)),
+                           [(mod.FesteringGob, (mod.MalodorousPervert,
+                                                   mod.ParrotDroppings))
+                            ],
+                           (mod.StupidGit, (object,)),
+                           [(mod.MalodorousPervert, (mod.StupidGit,)),
+                            [(mod.FesteringGob, (mod.MalodorousPervert,
+                                                    mod.ParrotDroppings))
+                             ]
+                            ]
+                           ]
+                          ])
+        tree = inspect.getclasstree([cls[1] for cls in classes], True)
         self.assertEqual(tree,
                          [(object, ()),
                           [(mod.ParrotDroppings, (object,)),