diff -r 27edae50e62c Include/objimpl.h
--- a/Include/objimpl.h	Sun Oct 09 20:19:21 2016 -0700
+++ b/Include/objimpl.h	Mon Oct 10 23:18:15 2016 +0900
@@ -256,7 +256,7 @@
     double dummy;  /* force worst-case alignment */
 } PyGC_Head;
 
-extern PyGC_Head *_PyGC_generation0;
+PyAPI_DATA(PyGC_Head *) _PyGC_generation0;
 
 #define _Py_AS_GC(o) ((PyGC_Head *)(o)-1)