diff -r d61e8050b7d7 setup.py
--- a/setup.py	Tue Dec 10 18:22:03 2013 -0800
+++ b/setup.py	Thu Dec 12 13:01:55 2013 +0100
@@ -39,6 +39,18 @@
     """Add the directory 'dir' to the list 'dirlist' (at the front) if
     1) 'dir' is not already in 'dirlist'
     2) 'dir' actually exists, and is a directory."""
+    if host_platform == 'darwin':
+        # Honor the MacOSX SDK setting when one was specified.
+        # An SDK is a directory with the same structure as a real
+        # system, but with only header files and libraries.
+        sysroot = macosx_sdk_root()
+
+        if dir is None:
+            return
+
+        if dir.startswith('/'):
+            dir = os.path.join(sysroot, dir[1:])
+
     if dir is not None and os.path.isdir(dir) and dir not in dirlist:
         dirlist.insert(0, dir)