Index: /pyyaml/trunk/setup.py
===================================================================
--- /pyyaml/trunk/setup.py	(revision 295)
+++ /pyyaml/trunk/setup.py	(revision 298)
@@ -50,4 +50,6 @@
 
 
+import sys, os.path
+
 from distutils import log
 from distutils.core import setup, Command
@@ -58,4 +60,10 @@
 from distutils.errors import CompileError, LinkError, DistutilsPlatformError
 
+if 'setuptools.extension' in sys.modules:
+    _Extension = sys.modules['setuptools.extension']._Extension
+    sys.modules['distutils.core'].Extension = _Extension
+    sys.modules['distutils.extension'].Extension = _Extension
+    sys.modules['distutils.command.build_ext'].Extension = _Extension
+
 try:
     from Pyrex.Distutils import Extension as _Extension
@@ -65,5 +73,4 @@
     with_pyrex = False
 
-import sys, os.path