diff -rpNu1 a/Lib/distutils/cmd.py b/Lib/distutils/cmd.py
--- a/Lib/distutils/cmd.py	2014-12-10 07:59:34.000000000 -0800
+++ b/Lib/distutils/cmd.py	2014-12-29 03:06:14.217957515 -0800
@@ -52,6 +52,6 @@ class Command:
         """
-        # late import because of mutual dependence between these classes
-        from distutils.dist import Distribution
-
-        if not isinstance(dist, Distribution):
+        # dist should quack like a Distribution (duck-typing avoids a
+        # circular dependency and hopefully ameliorates trouble due to
+        # setuptools having monkey patched distutils modules).
+        if not hasattr(dist, 'get_requires'):
             raise TypeError, "dist must be a Distribution instance"