Index: setuptools/command/build_ext.py
===================================================================
--- setuptools/command/build_ext.py     (revision 58493)
+++ setuptools/command/build_ext.py     (working copy)
@@ -74,7 +74,8 @@
         # Workaround for problems using some Pyrex versions w/SWIG and/or 2.4
         def swig_sources(self, sources, *otherargs):
             # first do any Pyrex processing
-            sources = _build_ext.swig_sources(self, sources) or sources
+            if hasattr(_build_ext, 'pyrex_sources'):
+                sources = _build_ext.pyrex_sources(self, sources, *otherargs)
             # Then do any actual SWIG stuff on the remainder
             return _du_build_ext.swig_sources(self, sources, *otherargs)