diff -r 388d58a5de9e Include/objimpl.h
--- a/Include/objimpl.h	Tue Sep 06 15:58:40 2016 -0700
+++ b/Include/objimpl.h	Tue Sep 06 17:11:43 2016 -0700
@@ -250,7 +250,7 @@
         union _gc_head *gc_prev;
         Py_ssize_t gc_refs;
     } gc;
-    double dummy;  /* force worst-case alignment */
+    long double dummy;  /* force worst-case alignment */
 } PyGC_Head;
 
 extern PyGC_Head *_PyGC_generation0;
diff -r 388d58a5de9e Objects/obmalloc.c
--- a/Objects/obmalloc.c	Tue Sep 06 15:58:40 2016 -0700
+++ b/Objects/obmalloc.c	Tue Sep 06 17:11:43 2016 -0700
@@ -643,8 +643,8 @@
  *
  * You shouldn't change this unless you know what you are doing.
  */
-#define ALIGNMENT               8               /* must be 2^N */
-#define ALIGNMENT_SHIFT         3
+#define ALIGNMENT               16               /* must be 2^N */
+#define ALIGNMENT_SHIFT         4
 
 /* Return the number of bytes in size class I, as a uint. */
 #define INDEX2SIZE(I) (((uint)(I) + 1) << ALIGNMENT_SHIFT)