Merged revisions 77791 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/branches/py3k

................
  r77791 | benjamin.peterson | 2010-01-26 20:25:58 -0600 (Tue, 26 Jan 2010) | 9 lines

  Merged revisions 77789 via svnmerge from
  svn+ssh://pythondev@svn.python.org/python/trunk

  ........
    r77789 | benjamin.peterson | 2010-01-26 20:16:42 -0600 (Tue, 26 Jan 2010) | 1 line

    raise a clear TypeError when trying to register a non-class
  ........
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diff --git a/Lib/abc.py b/Lib/abc.py
index f9b49ac..0f98036 100644
--- a/Lib/abc.py
+++ b/Lib/abc.py
@@ -94,7 +94,7 @@
 
     def register(cls, subclass):
         """Register a virtual subclass of an ABC."""
-        if not isinstance(cls, type):
+        if not isinstance(subclass, type):
             raise TypeError("Can only register classes")
         if issubclass(subclass, cls):
             return  # Already a subclass